Exhaust system for an engine

ABSTRACT

A snowmobile including: a frame; an engine supported by the frame; an exhaust pipe connected to the engine; and a turbocharger connected to the exhaust pipe. The turbocharger includes a bypass conduit fluidly communicating with the turbocharger housing and including an exhaust inlet fluidly connected to the exhaust pipe; a valve in the bypass conduit for controlling the flow of exhaust gas, and an exhaust collector. The valve is movable between first and second positions, a first flow path passing through the exhaust inlet, through the bypass conduit, and into the exhaust collector, a second flow path passing through the exhaust inlet, through the bypass conduit, through the exhaust turbine, and into the exhaust collector, in the first position, a majority of the exhaust gas flowing along the first flow path and in the second position, a majority of the exhaust gas flowing along the second flow path.

CROSS-REFERENCE

The present application is a continuation-in-part of InternationalPatent Application No. PCT/IB2019/054501, filed on May 30, 2019, whichclaims priority from U.S. Provisional Patent Application No. 62/678,922,filed on May 31, 2018, and from U.S. Provisional Patent Application No.62/783,576, filed on Dec. 21, 2018. The present application also claimspriority from U.S. Provisional Patent Application No. 62/958,787, filedon Jan. 9, 2020. The entirety of each of the above-mentioned documentsis incorporated by reference herein.

FIELD OF THE TECHNOLOGY

The present technology relates to engine exhaust systems.

BACKGROUND

For internal combustion engines, such as those used in snowmobiles, theefficiency of the combustion process can be increased by compressing theair entering the engine. This can be accomplished using a turbochargerconnected to the air intake and exhaust systems of the snowmobiles. Thecompression of the air by the turbocharger may be of particularimportance when the internal combustion engine is operated inenvironments where atmospheric pressure is low or when the air getsthinner.

The efficiency and the performance of some engines, especiallytwo-stroke engines, may however be hindered in certain circumstances bythe presence of a turbocharger because of an increased amount of backpressure caused by the turbocharger. Two-stroke engines tend to beespecially sensitive to non-optimal levels of back pressure.

There is thus a need for exhaust systems for internal combustion enginesthat can benefit from the addition of a turbocharger while overcomingsome of the previously known disadvantages of incorporating aturbocharger, including for example back pressure-related issues.

SUMMARY

It is an object of the present technology to ameliorate at least some ofthe inconveniences present in the prior art.

According to one aspect of the present technology, there is provided asnowmobile including an exhaust system which has a turbocharger and avalve controlling the flow of exhaust gas into the turbocharger. Thevalve, disposed in a conduit integrally connected or fastened to theturbocharger housing, directs the exhaust gas into the exhaust turbineof the turbocharger and/or allows exhaust gas through the bypass conduit(bypassing the turbocharger). The back pressure flowing into theturbocharger is generally higher than the pressure for entry of theexhaust gas entering the bypass such that the exhaust will generallyflow into the bypass, bypassing the turbocharger, when the valve isopened. The exhaust pipe fluidly connected to the engine, the bypassconduit, and an exhaust collector fluidly connected to a muffler are allgenerally aligned, such that exhaust gas bypassing the exhaust turbineflows generally freely to minimize back pressure.

The present technology also provides methods for controlling the flow ofexhaust gas through the exhaust system, in order to provide additionalair (and power) to the engine through use of the turbocharger in certainscenarios. The methods also provide for balance between rapidlyproviding the additional power and creating lag in the power increasethrough the creation of back pressure. The position of the valve,controlling flow into or bypassing the turbocharger, is adjustable tosend more or less exhaust gas into the turbocharger, depending onvarious parameters, in order to both increase air into the engine and tolimit the detrimental effects of increased back pressure on engineperformance. The valve divides the exhaust flow into two passages havingdifferent restriction levels (high back-pressure in turbo passage; lowback-pressure in turbo by-pass). Optimal control of the valve positionprovides optimization of the back-pressure to get maximum engine aircharging for increased power. This condition is normally only createdwith more time in a 2-strokes engines by the exhaust gas temperaturewarming up the tuned pipe. A improved engine response on then obtained.At the same time, having a portion of the exhaust gas flowing throughthe turbocharger, even when the turbocharger is not in use, allows arapid shift of the exhaust gas into the turbine inlet upon closure ofthe valve, in turn causing a rapid spool-up of the turbocharger,reducing turbo lag. The result of this valve control can improveresponse time and power of two-stroke engines, diminish the impact ofturbo back pressure and keep turbo lag at a minimum.

According to one aspect of the present technology, there is provided asnowmobile including a frame; at least one ski connected to the frame;an engine supported by the frame, the engine having an engine air inletand an exhaust outlet; an exhaust pipe fluidly connected to the exhaustoutlet of the engine; a turbocharger fluidly connected to the exhaustpipe, the turbocharger including: an exhaust turbine, and a housing theexhaust turbine; a bypass conduit disposed upstream of the housing andfluidly communicating with the housing, the bypass conduit including anexhaust inlet fluidly connected to the exhaust pipe; a valve disposed inthe bypass conduit for selectively controlling the flow of exhaust gasthrough the turbocharger, the valve being selectively movable between atleast a first position and a second position; and an exhaust collectorfluidly connected to the turbine housing and the bypass conduit forreceiving a flow of exhaust gas therefrom, a first exhaust flow pathbeing defined from the exhaust inlet to the exhaust collector, exhaustgas flowing along the first exhaust flow path passing through theexhaust inlet, then through the bypass conduit, and then into theexhaust collector, a second exhaust flow path being defined from theexhaust inlet to the exhaust collector, exhaust gas flowing along thesecond exhaust flow path passing through the exhaust inlet, then throughthe bypass conduit, then through the exhaust turbine, and then into theexhaust collector, in the first position of the valve, at least amajority of the exhaust gas flowing along the first exhaust flow path,in the second position of the valve, at least a majority of the exhaustgas flowing along the second exhaust flow path.

In some implementations, the valve is selectively moved to the secondposition when the engine is operated below a threshold atmosphericpressure.

In some implementations, the valve is further selectively movable to atleast one intermediate position between the first and second positions;and in the at least one intermediate position, the exhaust gas flowsalong both of the first exhaust flow path and the second exhaust flowpath.

In some implementations, the turbocharger further includes an aircompressor fluidly connected to the engine air inlet; and the snowmobilefurther includes an air intake system fluidly connecting atmosphere tothe engine, the air intake system including: the air compressor, and theengine air inlet.

In some implementations, the exhaust collector includes a singlecollector outlet; and the snowmobile further includes a muffler fluidlyconnected to the collector outlet, the muffler receiving the exhaust gasfrom both the first exhaust flow path and second exhaust flow path viathe collector outlet.

In some implementations, the exhaust collector includes a collectoroutlet; and the snowmobile further includes a muffler fluidly connectedto the collector outlet, the muffler having a single muffler inlet forreceiving exhaust gas from both the first exhaust flow path and secondexhaust flow path via the collector outlet.

In some implementations, the exhaust collector includes: at least oneinlet for receiving exhaust gas flow, the at least one inlet including:a first portion for receiving exhaust gas flowing along the firstexhaust flow path; and a second portion for receiving exhaust gasflowing along the second exhaust flow path, the first portion and thesecond portion being integrally connected.

In some implementations, the engine includes: a throttle valve, and athrottle valve position sensor operatively connected to the throttlevalve; and the valve is selectively moved based at least on a throttlevalve position determined by the throttle valve position sensor.

In some implementations, the engine includes: a throttle valve, and athrottle valve position sensor operatively connected to the throttlevalve; and the valve is selectively moved based at least on a rate ofchange of a throttle valve position, the rate of change being determinedby the throttle valve position sensor.

In some implementations, the bypass conduit includes a passage throughwhich exhaust gas flows when flowing along the first exhaust flow path;the exhaust turbine has a turbine inlet through which exhaust gas flowswhen flowing along the second exhaust flow path; and a cross-sectionalarea of the passage is larger than a cross-sectional area of the turbineinlet of the turbocharger.

In some implementations, a change of direction of exhaust gas flowingfrom an outlet of the exhaust pipe along the second exhaust flow path isgreater than for exhaust gas flowing from the outlet of the exhaust pipealong the first exhaust flow path bypassing the exhaust turbine.

According to another aspect of the present technology, there is provideda method of supplying a fuel-air mixture in an engine of a vehicle. Themethod includes determining a pressure differential between an intakeair pressure of air flowing toward the engine and an exhaust gaspressure of exhaust gas flowing out of the engine; determining, based onat least the pressure differential, an amount of fuel to be injectedinto the engine; and injecting the amount of fuel into the engine.

In some implementations, determining the pressure differentialcomprises: determining the intake air pressure; and determining theexhaust gas pressure.

In some implementations, the method further includes determining anengine speed; and wherein the amount of fuel to be injected is furtherdetermined based on the engine speed.

In some implementations, the method further includes determining athrottle position; and wherein the amount of fuel to be injected isfurther determined based on the throttle position.

In some implementations, the method further includes determining achanged pressure differential; determining, based on at least thechanged pressure differential, a revised amount of fuel to be injectedinto the engine; and injecting the revised amount of fuel into theengine.

In some implementations, the method further includes determining thatthe pressure differential has increased; determining, based on at leastthe pressure differential having increased, a reduced amount of fuel tobe injected into the engine; and injecting the reduced amount of fuelinto the engine.

In some implementations, the method further includes determining thatthe pressure differential has decreased; determining, based on at leastthe pressure differential having decreased, a reduced amount of fuel tobe injected into the engine; and injecting the reduced amount of fuelinto the engine.

According to another aspect of the present technology, there is provideda snowmobile including a frame; at least one ski connected to the frame;an engine supported by the frame, the engine having an engine exhaustoutlet; a turbocharger fluidly connected to the engine exhaust outlet;an oil reservoir fluidly connected to the turbocharger; and an oil pumpfluidly connected between the oil reservoir and the turbocharger, theoil pump supplying oil from the oil reservoir to the turbocharger, theturbocharger being fluidly connected to the engine for supplying oilfrom the turbocharger to the engine.

In some implementations, the oil pump additionally supplies oil from theoil reservoir to the engine.

In some implementations, the oil pump is a first oil pump; and furtherincluding a second oil pump fluidly connected between the turbochargerand the engine, the second oil pump supplying oil from the turbochargerto the engine.

In some implementations, the first oil pump additionally supplies oilfrom the oil reservoir to the engine.

In some implementations, the engine includes at least one exhaust valve;the first oil pump supplies oil from the oil reservoir to the at leastone exhaust valve and to the turbocharger; and the second oil pumpsupplies oil from the turbocharger to the at least one exhaust valve.

In some implementations, the engine includes a crankshaft; and the firstoil pump additionally supplies oil from the oil reservoir to thecrankshaft.

In some implementations, the first oil pump comprises four outlet ports;two of the four outlet ports supply oil to the crankshaft; one of thefour outlet ports supply oil to the at least one exhaust valve; and oneof the four outlet ports supply oil to the turbocharger.

In another aspect of the present technology, there is provided asnowmobile including a frame; at least one ski connected to the frame;an engine supported by the frame, the engine having an engine air inletand an exhaust outlet; an exhaust pipe fluidly connected to the exhaustoutlet of the engine; a turbocharger fluidly connected to the exhaustpipe, the turbocharger including an exhaust turbine, and a housing theexhaust turbine; a bypass conduit disposed upstream of the housing andfluidly communicating with the housing, the bypass conduit being fluidlyconnected to an outlet of the exhaust pipe; a valve disposed in thebypass conduit for selectively controlling the flow of exhaust gasthrough the turbocharger by selectively closing a bypass passage withinthe bypass conduit, the valve having at least a bypass position foropening the bypass passage and directing exhaust gas to bypass theexhaust turbine; and an exhaust collector fluidly connected to thebypass conduit for receiving a flow of exhaust gas therefrom, at least aportion of an inlet of the exhaust collector being contained within aprojection of the outlet of the exhaust pipe, the projection being takenalong an axis normal to the outlet of the exhaust pipe.

According to yet another aspect of the present technology, there isprovided a turbocharger assembly for fluidly connecting to an exhaustpipe. The assembly includes a turbocharger including: an exhaustturbine, and a housing the exhaust turbine; and a bypass conduitdisposed upstream of the housing and fluidly communicating with thehousing, the bypass conduit including: a conduit inlet for receivingexhaust gas from the exhaust pipe, the conduit inlet being defined bythe bypass conduit, the conduit inlet defining a flow axis through acenter of the conduit inlet, the exhaust gas flowing into the conduitinlet flowing generally parallel to the flow axis; a bypass passagedefined by the bypass conduit, the bypass passage forming a fluidconnection between the conduit inlet and a bypass outlet defined by thebypass conduit; a valve disposed in the bypass conduit for selectivelycontrolling the flow of exhaust gas through the bypass passage, thevalve being selectively movable between at least an open position and aclosed position; and a turbocharger passage defined by the bypassconduit, the turbocharger passage forming a fluid connection between theconduit inlet and the exhaust turbine, the conduit inlet and an inlet ofthe bypass passage being at least partially aligned such that at least aportion of the exhaust gas entering the conduit inlet parallel to theflow axis flows unobstructed into the bypass passage when the valve isin the open position.

In some implementations, when the valve is in the closed position, atleast a portion of the valve is contacted by the exhaust gas enteringthrough the conduit inlet and flowing parallel to the flow axis.

In some implementations, when the valve is in a position intermediatethe open position and the closed position, at least a portion of thevalve is contacted by the exhaust gas entering through the conduit inletand flowing parallel to the flow axis.

According to yet another aspect of the present technology, there isprovided a conduit for fluidly connecting to a turbocharger housing. Theconduit includes an inlet conduit portion for receiving exhaust gas froman exhaust pipe; an inlet defined by the inlet conduit portion, exhaustgas from the exhaust pipe entering the inlet conduit portion through theinlet, the inlet defining a central axis normal to the inlet and througha center of the inlet; a first outlet conduit portion; a second outletconduit portion; and a flow divider disposed between the first outletconduit portion and the second outlet conduit portion, the flow dividerbeing disposed between the central axis and one of the first outletconduit portion and the second outlet conduit portion.

In some implementations, the inlet conduit portion, the first outletconduit portion, and the second outlet conduit portion are integrallyconnected; and the inlet conduit portion, the first outlet conduitportion, and the second outlet conduit portion form a generally Y-shapedconduit.

In some implementations, the inlet is a circle; and the central axispasses through the center of the circle.

In some implementations, the first outlet conduit portion is fluidlyconnected to a turbocharger disposed within the turbocharger housing;exhaust gas exiting the conduit through the second outlet conduitportion bypasses the turbocharger; and the flow divider is disposedbetween the central axis and the second outlet conduit portion.

In some implementations, the conduits further includes a valve disposedin the second outlet conduit portion; and wherein the valve isselectively movable between at least: a first position allowing exhaustgas to enter the second outlet conduit portion, and a second positionblocking exhaust gas from entering the second outlet conduit portion.

According to yet another aspect of the present technology, there isprovided a turbocharger assembly for fluidly connecting to an exhaustpipe. The assembly includes a turbocharger including: an exhaustturbine, a turbocharger inlet defined by the exhaust turbine, and ahousing the exhaust turbine; and a bypass conduit disposed upstream ofthe housing and fluidly communicating with the housing, the bypassconduit including: a conduit inlet for receiving exhaust gas from theexhaust pipe; a bypass passage forming a fluid connection between theconduit inlet and a bypass outlet defined by the bypass conduit, thebypass passage including an opening; and a turbocharger passage forminga fluid connection between the conduit inlet and the turbocharger inlet,an area of the opening being between 0.75 and 1.25 times an area of theturbocharger inlet.

In some implementations, the area of the opening is greater than thearea of the turbocharger inlet.

In some implementations, the area of the turbocharger inlet is greaterthan the area of the opening.

According to yet another aspect of the present technology, there isprovided a method for controlling a flow of exhaust gas from an engine.The method includes determining a pressure; and moving, based at leaston the pressure, a valve fluidly connected within an exhaust flow path:a first position such that at least a majority of the exhaust gas flowsalong a first exhaust flow path bypassing an exhaust turbine of aturbocharger; a second position such that at least a majority of theexhaust gas flows along a second exhaust flow path passing through theexhaust turbine; and at least one intermediate position between thefirst position and the second position, such that exhaust gas flowspartially along the first exhaust flow path and partially along thesecond exhaust flow path.

In some implementations, determining the pressure includes determining apressure differential; and determining the pressure differentialincludes: determining a predetermined boost pressure of air flowing intothe engine, and determining an actual boost pressure of air flowing intothe engine.

In some implementations, determining the actual boost pressure includesdetermining, by a first sensor, an intake air pressure of air flowing tothe engine.

In some implementations, determining the predetermined boost pressureincludes at least one of: determining a throttle lever position; anddetermining a rate of throttle valve opening.

In some implementations, determining the predetermined boost pressureincludes at least one of: determining a throttle lever position;determining an engine speed; and determining a rate of throttle valveopening.

In some implementations, the method further includes determining thatthe difference between the predetermined boost pressure and the actualboost pressure is less than a difference threshold; based on thedifference being less than the difference threshold, determining adesired valve position of the valve from a fine adjustment data setrelating to fine adjustments to pressure, the fine adjustment data setproviding the desired valve position for decreasing the differencebetween the predetermined boost pressure and the actual boost pressure,the fine adjustment data set being based at least one of throttleposition and the engine speed; and moving, following determining thedesired valve position, the valve toward the desired valve position.

In some implementations, determining the pressure includes determining apressure differential; and further including determining that thepressure differential is greater than a difference threshold;determining, based on the pressure differential being greater than thedifference threshold, a desired valve position of the valve from acoarse adjustment data set relating to coarse adjustments to pressure,the coarse adjustment data set providing the desired valve position fordecreasing the difference between the requested boost pressure and theintake pressure, the coarse adjustment data set being based at least oneof throttle position and the engine speed; and moving, followingdetermining the desired valve position, the valve toward the desiredvalve position.

In some implementations, determining the pressure includes: determining,by a first sensor, an intake air pressure of air flowing to the engine,and determining, by a second sensor, an exhaust gas pressure of exhaustgas flowing out of the engine; and the method further includes:determining a predetermined pressure differential between the exhaustgas pressure and the intake air pressure; and determining that adifference between the pressure differential and the predeterminedpressure differential is non-zero; and moving the valve based on atleast the pressure includes moving the valve based at least on thedifference being non-zero and moving the valve to one of: the secondposition; and the at least one intermediate position.

In some implementations, the predetermined pressure differential isdetermined based on throttle position and engine speed.

According to yet another aspect of the present technology, there isprovided a method for controlling a flow of exhaust gas from an engine.The method includes determining, by a throttle position sensor, athrottle position; determining, by an engine sensor, an engine speed ofthe engine; moving, based at least on one of the throttle position andthe engine speed, a valve fluidly connected between a turbocharger andthe engine to one of: a first position such that at least a majority ofthe exhaust gas flows along a first exhaust flow path bypassing anexhaust turbine of the turbocharger; a second position such that atleast a majority of the exhaust gas flows along a second exhaust flowpath passing through the exhaust turbine; and at least one intermediateposition between the first position and the second position, such thatexhaust gas flows partially along the first exhaust flow path andpartially along the second exhaust flow path.

In some implementations, moving the valve is based on at least one ofthe throttle position, the engine speed, and a temperature of an exhaustpipe operatively connected to the engine.

In some implementations, the method further includes determining apressure differential by: determining a predetermined boost pressure ofair flowing into the engine, the predetermined boost pressure isdetermined based at least on one of the throttle position and the enginespeed, and determining an actual boost pressure of air flowing into theengine; and wherein moving the valve is further based on the pressuredifferential.

In some implementations, determining the actual boost pressure includesdetermining, by a first sensor, an intake air pressure of air flowing tothe engine.

In some implementations, the method further includes determining atemperature of an exhaust pipe disposed upstream from the valve; andwherein moving the valve is further based on the temperature of theexhaust pipe.

In some implementations, the method further includes, prior to movingthe valve: determining if the engine is operating at low altitude orhigh altitude; retrieving, upon determining the engine is operating atlow altitude, a desired valve position from a low altitude data set;retrieving, upon determining the engine is operating at high altitude, adesired valve position from a high altitude data set; and wherein:moving the valve includes moving the valve to the desired position, thedesired position being one of the first position, the second position,and the at least one intermediate position.

In some implementations, the method further includes determining if theengine is operating at low altitude or high altitude includesdetermining, by a first pressure sensor, an atmospheric pressure.

In some implementations, the method further includes determining, basedat least on the throttle position and the engine speed, a thresholdpressure differential of the engine; determining an actual pressuredifferential of the engine; determining that the actual pressuredifferential is greater than the threshold pressure differential; andmoving, based at least on the actual pressure differential being greaterthan the threshold pressure differential, the valve toward the firstposition if the valve is one of the second position and the at least oneintermediate position.

In some implementations, determining the actual pressure differential ofthe engine includes determining, by an exhaust pressure sensor, anexhaust pressure downstream of the engine; determining, by an air intakesensor, an air intake pressure upstream of the engine; and determiningthe difference of the exhaust pressure and the air intake pressure.

According to yet another aspect of the present technology, there isprovided a method for controlling a flow of exhaust gas from an engine.The method includes determining that an exhaust gas pressure of airflowing out of the engine is above a threshold exhaust gas pressure, avalve fluidly connected between a turbocharger and the engine being in afirst position such that at least a majority of the exhaust gas flowsalong a first exhaust flow path passing through an exhaust turbine ofthe turbocharger; and moving the valve, based at least on the exhaustgas pressure being above the threshold exhaust gas pressure, to one of:a second position such that at least a majority of the exhaust gas flowsalong a second exhaust flow path bypassing through the exhaust turbine;and at least one intermediate position between the first position andthe second position, such that exhaust gas flows partially along thefirst exhaust flow path and partially along the second exhaust flowpath.

For purposes of this application, terms related to spatial orientationsuch as forwardly, rearward, upwardly, downwardly, left, and right, areas they would normally be understood by a driver of the snowmobilesitting thereon in a normal riding position. Terms related to spatialorientation when describing or referring to components or sub-assembliesof the snowmobile, separately from the snowmobile, such as a heatexchanger for example, should be understood as they would be understoodwhen these components or sub-assemblies are mounted to the snowmobile,unless specified otherwise in this application.

Implementations of the present technology each have at least one of theabove-mentioned object and/or aspects, but do not necessarily have allof them. It should be understood that some aspects of the presenttechnology that have resulted from attempting to attain theabove-mentioned object may not satisfy this object and/or may satisfyother objects not specifically recited herein. The explanations providedabove regarding the above terms take precedence over explanations ofthese terms that may be found in any one of the documents incorporatedherein by reference.

Additional and/or alternative features, aspects and advantages ofimplementations of the present technology will become apparent from thefollowing description, the accompanying drawings and the appendedclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present technology, as well as otheraspects and further features thereof, reference is made to the followingdescription which is to be used in conjunction with the accompanyingdrawings, where:

FIG. 1 is a left side elevation view of a snowmobile;

FIG. 2 is a top, rear, right side perspective view of an engine, airintake system and exhaust system of the snowmobile of FIG. 1;

FIG. 3 is a front elevation view of the engine, air intake system andexhaust system of FIG. 2;

FIG. 4 is a cross-sectional view of the engine and some portions of theair intake system and the exhaust system of FIG. 2;

FIG. 5 is a top plan view of portions of the air intake system and theexhaust system of FIG. 2;

FIG. 6 is a schematic representation of a lubrication system of thesnowmobile of FIG. 1;

FIG. 7 is a schematic diagram of lubricating oil flow of the lubricationsystem of FIG. 6;

FIG. 8 is a schematic representation of the exhaust system of FIG. 2;

FIG. 9 is a close-up view of the portions of the air intake system andexhaust system of FIG. 5;

FIG. 10 is a right side elevation view of portions of the air intakesystem and the exhaust system of FIG. 2;

FIG. 11 is a close-up view of the portions of the air intake system andexhaust system of FIG. 10;

FIG. 12 is a front elevation view of a turbocharger, a bypass conduit,and an exhaust collector of the exhaust system of FIG. 2;

FIG. 13 is a perspective view of the bypass conduit of FIG. 12, shown inisolation;

FIG. 14 is a cross-sectional view of the bypass conduit of FIG. 12,taken along line 14-14 of FIG. 13, with a valve in a closed position;

FIG. 15 is the cross-sectional view of FIG. 14, with the valve in anopen position;

FIG. 16 is the cross-sectional view of FIG. 14, with the valve in anintermediate position;

FIG. 17 is a perspective view of portions of the turbocharger and thebypass conduit of FIG. 12, with a portion of the top of the bypassconduit and the valve having been removed;

FIG. 18 is a top plan view of the turbocharger and bypass conduit ofFIG. 12;

FIG. 19 is a cross-sectional view of the turbocharger of FIG. 18, takenalong line 19-19 of FIG. 18;

FIG. 20A is a left side elevation view of the exhaust collector of FIG.12, shown in isolation;

FIG. 20B is a top, right side perspective view of the exhaust collectorof FIG. 20A;

FIG. 20C is a bottom plan view of the exhaust collector of FIG. 20A;

FIG. 21 is a flowchart illustrating a method, according to the presenttechnology, of controlling exhaust gas flow through the exhaust systemof FIG. 2;

FIG. 22 is a flowchart illustrating another method according to thepresent technology of controlling exhaust gas flow through the exhaustsystem of FIG. 2;

FIG. 23 is a flowchart illustrating another method according to thepresent technology of controlling exhaust gas flow through the exhaustsystem of FIG. 2;

FIG. 24 is a flowchart illustrating a method according to the presenttechnology for providing a fuel-air mixture to the engine of FIG. 2;

FIG. 25 is a cross-sectional view of the bypass conduit of FIG. 12,taken along line 25-25 of FIG. 13, with the valve in the open position;

FIG. 26 is an elevation view of an upstream side of the valve of FIG.14;

FIG. 27 is an elevation view of a downstream side of the valve of FIG.26;

FIG. 28 is a cross-sectional view of the valve of FIG. 26, taken alongline 28-28 of FIG. 27;

FIG. 29 is a cross-sectional view of the valve of FIG. 26, taken alongline 29-29 of FIG. 27;

FIG. 30 is a chart representing a percentage mass flow through anopening as a function of a position of a valve;

FIG. 31 is a flowchart representing an illustrative scenario ofcontrolling exhaust gas flow through the exhaust system of FIG. 2;

FIG. 32 illustrates an example dataset for use in the illustrativescenario of FIG. 31;

FIG. 33 illustrates additional example datasets for use in theillustrative scenario of FIG. 31;

FIG. 34 illustrates example datasets used in the method of FIG. 24;

FIG. 35 is a partial cut-away view of an airbox of the air intake systemof FIG. 2, with a portion of a left side of the airbox having beenremoved;

FIG. 36 is a partial cut-away view of the airbox of FIG. 35, with aportion of a rear side of the airbox having been removed;

FIG. 37 is a perspective view of a main inlet member of the airbox ofFIG. 35, showing a bypass valve of the airbox in a closed state;

FIG. 38 is a perspective view of the main inlet member of the airbox ofFIG. 37, showing the bypass valve in an open state;

FIG. 39 is a cross-sectional view of the main inlet member and thebypass valve of FIG. 38;

FIG. 40 is an exploded view of the main inlet member and the bypassvalve of FIG. 37; and

FIG. 41 is a rear elevation view of the engine and air intake system ofFIG. 2, showing two different intake air flow paths.

It should be noted that the Figures may not be drawn to scale, exceptwhere otherwise noted.

DETAILED DESCRIPTION

The present technology is described herein with respect to a snowmobile10 having an internal combustion engine and two skis. However, it iscontemplated that some aspects of the present technology may apply toother types of vehicles such as, but not limited to, snowmobiles with asingle ski, road vehicles having two, three, or four wheels, off-roadvehicles, all-terrain vehicles, side-by-side vehicles, and personalwatercraft.

With reference to FIGS. 1 and 2, a snowmobile 10 according to thepresent technology will be described. The snowmobile 10 includes aforward end 12 and a rearward end 14. The snowmobile 10 includes avehicle body in the form of a frame or chassis 16 which includes atunnel 18, an engine cradle portion 20, a front suspension module 22 andan upper structure 24.

An internal combustion engine 26 is carried in an engine compartmentdefined in part by the engine cradle portion 20 of the frame 16. A fueltank 28, supported above the tunnel 18, supplies fuel to the engine 26for its operation. The engine 26 receives air from an air intake system100. The engine 26 and the air intake system 100 are described in moredetail below.

An endless drive track 30 is positioned at the rear end 14 of thesnowmobile 10. The drive track 30 is disposed generally under the tunnel18, and is operatively connected to the engine 26 through a belttransmission system and a reduction drive. The endless drive track 30 isdriven to run about a rear suspension assembly 32 operatively connectedto the tunnel 18 for propulsion of the snowmobile 10. The endless drivetrack 30 has a plurality of lugs 31 extending from an outer surfacethereof to provide traction to the track 30.

The rear suspension assembly 32 includes drive sprockets 34, idlerwheels 36 and a pair of slide rails 38 in sliding contact with theendless drive track 30. The drive sprockets 34 are mounted on an axle 35and define a sprocket axis 34 a. The axle 35 is operatively connected toa crankshaft 126 (see FIG. 3) of the engine 26. The slide rails 38 areattached to the tunnel 18 by front and rear suspension arms 40 and shockabsorbers 42. It is contemplated that the snowmobile 10 could beprovided with a different implementation of a rear suspension assembly32 than the one shown herein.

A straddle seat 60 is positioned atop the fuel tank 28. A fuel tankfiller opening covered by a cap 92 is disposed on the upper surface ofthe fuel tank 28 in front of the seat 60. It is contemplated that thefuel tank filler opening could be disposed elsewhere on the fuel tank28. The seat 60 is adapted to accommodate a driver of the snowmobile 10.The seat 60 could also be configured to accommodate a passenger. Afootrest 64 is positioned on each side of the snowmobile 10 below theseat 60 to accommodate the driver's feet.

At the front end 12 of the snowmobile 10, fairings 66 enclose the engine26 and the belt transmission system, thereby providing an external shellthat not only protects the engine 26 and the transmission system, butcan also make the snowmobile 10 more aesthetically pleasing. Thefairings 66 include a hood 68 and one or more side panels which can beopened to allow access to the engine 26. A windshield 69 connected tothe fairings 66 acts as a wind screen to lessen the force of the air onthe rider while the snowmobile 10 is moving.

Two skis 70 positioned at the forward end 12 of the snowmobile 10 areattached to the front suspension module 22 of the frame 16 through afront suspension assembly 72. The front suspension module 22 isconnected to the front end of the engine cradle portion 20. The frontsuspension assembly 72 includes ski legs 74, supporting arms 76 and balljoints (not shown) for operatively connecting to the respective ski leg74, supporting arms 76 and a steering column 82 (schematicallyillustrated).

A steering assembly 80, including the steering column 82 and a handlebar84, is provided generally forward of the seat 60. The steering column 82is rotatably connected to the frame 16. The lower end of the steeringcolumn 82 is connected to the ski legs 74 via steering rods (not shown).The handlebar 84 is attached to the upper end of the steering column 82.The handlebar 84 is positioned in front of the seat 60. The handlebar 84is used to rotate the steering column 82, and thereby the skis 70, inorder to steer the snowmobile 10. A throttle operator 86 in the form ofa thumb-actuated throttle lever is mounted to the right side of thehandlebar 84. Other types of throttle operators, such as afinger-actuated throttle lever and a twist grip, are also contemplated.A brake actuator 88, in the form of a hand brake lever, is provided onthe left side of the handlebar 84 for braking the snowmobile 10 in aknown manner. It is contemplated that the windshield 69 could beconnected directly to the handlebar 84.

At the rear end of the snowmobile 10, a snow flap 94 extends downwardfrom the rear end of the tunnel 18. The snow flap 94 protects againstdirt and snow that can be projected upward from the drive track 30 whenthe snowmobile 10 is being propelled by the moving drive track 30. It iscontemplated that the snow flap 94 could be omitted.

The snowmobile 10 includes other components such as a display cluster,and the like. As it is believed that these components would be readilyrecognized by one of ordinary skill in the art, further explanation anddescription of these components will not be provided herein.

With additional reference to FIGS. 2 to 6, the engine 26 and the airintake system 100 will be described in more detail. Air from theatmosphere surrounding the snowmobile 10 flows through side apertures113 defined in an upper portion 25 of the upper structure 24 of thechassis 16. The air then flows into a secondary airbox 110. Thesecondary airbox 110 is disposed above the front suspension module 22. Agenerally Y-shaped conduit 118 (FIG. 2) fluidly connects the secondaryairbox 110, via a conduit portion 117, to a compressor inlet 312 of anair compressor 310 (FIG. 5) disposed on the right side of the engine 26.The conduit 118 further fluidly connects to an inlet 119 of a primaryairbox 120 via a conduit portion 121. The inlet 119 is defined by a maininlet member 210 of the primary airbox 120. The main inlet member 210 isconnected to a body of the primary airbox 120 in part by various tabs213 (FIG. 37) disposed along a periphery of the main inlet member 210The primary airbox 120 includes a bypass valve 123 (see FIGS. 35, 36 and37 to 40) controlling air flow through the inlet 119 into the primaryairbox 120. As will be described in greater detail below, the bypassvalve 123 is mounted to the main inlet member 210 of the primary airbox120. It is contemplated that the secondary airbox 110 could be omittedand that air from the atmosphere could directly enter into the inlet 312and/or the inlet 119 of the primary airbox 120 without going through thesecondary airbox 110.

Air from the environment entering the snowmobile 10, passing through theair compressor 310, and flowing into the engine 26 generally follows anintake air flow path 444, illustrated schematically in FIG. 41. Air fromthe atmosphere, passing through the secondary airbox 110 and into theair compressor 310 via the conduit 118 and inlet 312, is compressed bythe air compressor 310. The compressed air then flows out of the aircompressor 310 through an outlet 314, into a conduit 316 and into aninlet 317 (FIG. 35) of the primary airbox 120. As shown in FIG. 35, theinlet 317 is defined by an inlet projection 319 of the main inlet member210 of the primary airbox 120. As can be seen in FIGS. 35 and 37, theopenings forming the inlets 119, 317 of the primary airbox 120 areoriented such that their respective central axes extend parallel to oneanother. The primary airbox 120 is fluidly connected to the engine 26via two air outlets 122 of the primary airbox 120 (see also FIG. 10).

The bypass valve 123 of the primary airbox 120 is spring-loaded to aclosed position, such that air is preferentially received from the aircompressor 310 via the conduit 316. When the air pressure within theprimary airbox 120 falls below a threshold value, for example when theengine 26 is rotating at a speed that requires more air than isavailable in the primary airbox 120, the bypass valve 123 opens to allowair from the atmosphere, via the secondary airbox 110, to enter theprimary airbox 120 directly. In some situations, this can aid inobtaining optimal operation of the engine 26, especially when theturbocharger 300 is spooling and not supplying the necessary air flow tothe primary airbox 120 for the air being requested by the engine 26.

With reference to FIGS. 35 to 40, the bypass valve 123 has a valve body124 that is movable between closed and open positions to respectivelyclose and open the inlet 119 of the primary airbox 120. As shown in FIG.39, the valve body 124 has a conical portion 132 and a hollow stemportion 134 extending from the conical portion 132. The conical portion132 has a round periphery 133 to match the round shape of the inlet 119.In this embodiment, the valve body 124 is made of a composite material,and in particular a polymeric composite material. Notably, the materialof the valve body 124 is a fiber-reinforced polymer. Specifically, inthis embodiment, the valve body 124 is made of a polypropylene andfibers embedded therein. A valve safety member 136 is connected to thevalve body 124 to prevent pieces of the valve body 124 from flowing intothe engine 26 in case the valve body 124 were to break or chip duringoperation. The valve safety member 136 is disposed on an inner side ofthe valve body 124 (i.e., the side of the valve body 124 facing inwardlyinto the primary airbox 120), and specifically is mated to the conicalportion 132 of the valve body 124. Notably, the safety member 136 isovermolded onto the conical portion 132 of the valve body 124. In thisembodiment, the valve safety member 136 is made of a thermoplasticelastomer material. For instance, the valve safety member 136 may bemade of Santoprene®.

The valve body 124 is operatively connected to the main inlet member 210of the primary airbox 120. In particular, the valve body 124 issupported by a valve support 216 of the main inlet member 210. The valvesupport 216 is disposed on an inner side 212 of the main inlet member210 (opposite an outer side 214 of the main inlet member 210) andincludes three arms 218 connected to one another at a central junction219 and to an inner surface 217 of the main inlet member 210. As shownin FIGS. 37 and 38, the arms 218 extend radially from the centraljunction 219 at equal angles from one another. A central axis 215extending through a center of a circular opening 220 of the main inletmember 210 (which corresponds to the inlet 119 of the primary airbox120) also extends through the central junction 219. As shown in FIGS. 39and 40, a post 223 extends outwardly from the central junction 219 ofthe valve support 216, along the central axis 215 toward the opening220. As shown in FIG. 39, the post 223 is received in part within thehollow stem portion 134 of the valve body 124. The post 223 is sizedsuch that the stem portion 134 and the post 223 are in a slidingrelationship to allow the stem portion 134, and therefore the valve body124 to move relative to the post 223.

As shown in FIGS. 39 and 40, an outer inlet member 222 is disposed onthe outer side 214 of the main inlet member 210. The outer inlet member222 has a central portion 224 and a flange portion 226 extendingradially outwardly from the central portion 224 at one end thereof. Thecentral portion 224 defines a central opening 228 that is concentricallyaligned with the opening 220 of the main inlet member 210. The flangeportion 226 defines a plurality of fastener openings (not shown) forreceiving respective fasteners 230 (FIG. 40). Notably, the fasteners 230extends through the flange portion 226 and threadedly engage respectivefastener mounts 232 (FIGS. 37, 38) of the main inlet member 210 tosecure the outer inlet member 222 to the main inlet member 210.Moreover, a generally annular sealing member 234 is disposed in partbetween the flange portion 226 of the outer inlet member 222 and themain inlet member 210. The sealing member 234 has a central inner lip235 extending inwardly into the opening 220 defined by the main inletmember 210. The inner lip 235 of the sealing member 234 is configured tocontact the valve body 124 when the valve body 124 is in the closedposition to form a seal therewith. As such, the contact between thesealing member 234 and the conical portion 132 of the valve body 124prevents air from flowing through the inlet 119. In this embodiment, thesealing member 234 is made of rubber.

As shown in FIGS. 39 and 40, the bypass valve 123 includes a spring 125that is mounted to the post 223 of the valve support 216. The spring 125is disposed between the valve body 124 and the central junction 219 ofthe valve support 216. As such, the spring 125 normally biases the valvebody 124 to the closed position. The spring constant of the spring 125is chosen such that the bypass valve 123 will open and close at apredetermined pressure within the primary airbox 120. Thus once opened,the bypass valve 123 will automatically close (i.e., the valve body 124will move to the closed position) when the airflow from the turbocharger300 increases the pressure within the primary airbox 120 to thepredetermined pressure, and vice versa. The diameter of the valve body124 is sized to allow for a high flow capacity between the secondary andprimary airboxes 110, 120. This aids in ensuring optimal pressure withinprimary airbox 120 and thus aids optimal engine performance in generallyall situations even if turbocharger 300 is not spooled.

As can be seen in FIG. 41, a distance travelled by intake air to theengine 26 is shorter when the intake air flows through the bypass valve123 along a flow path 445 than when it flows through the turbocharger300 along the flow path 444. More specifically, the conduit portion 121and the bypass valve 123 reduce the air flow travel distance between thesecondary airbox 110 and the primary airbox 120, when compared to theair flow travel distance through the conduit portion 117, theturbocharger 300 and the conduit 316. As such, depending on the airpressure within primary airbox 120, the airflow between the secondaryand primary airboxes 110, 120 has either a short airflow path or a longairflow path available. Moreover, as shown in FIG. 41, each of theconduit portions 117, 121 and the conduit 316 along which the flow paths445, 444 respectively pass through at least partially overlap the engine26 in front and rear elevation views thereof. That is, the conduitportions 117, 121 of the conduit 118 and the conduit 316 are, at leastin part, laterally and vertically aligned with the engine 26. Inclusionof the bypass valve 123 in the primary airbox 120 further allows theengine 26 to be operated in either a turbocharged mode or a naturallyaspirated mode. Operation of the engine 26, and corresponding operationof the turbocharger 300, in order to operate in the two modes will bedescribed in further detail below.

The engine 26 is an inline, two-cylinder, two-stroke, internalcombustion engine. The two cylinders of the engine 26 are oriented withtheir cylindrical axes disposed vertically. It is contemplated that theengine 26 could be configured differently. For example, the engine 26could have more or less than two cylinders, and the cylinders could bearranged in a V-configuration instead of in-line. It is contemplatedthat in some implementations the engine 26 could be a four-strokeinternal combustion engine, a carbureted engine, or any other suitableengine capable of propelling the snowmobile 10. The engine 26 includesan engine coolant system 23 to aid in cooling the engine 26. The enginecoolant system 23 includes an engine coolant temperature sensor (notshown) for monitoring the temperature of the engine coolant circulatingin the engine coolant system 23.

As shown in FIGS. 1, 2, and 4, the engine 26 receives air from the airintake system 100, specifically the outlets 122 of the primary airbox120, via engine air inlets 27 defined in the rear portion of eachcylinder of the engine 26. Each air inlet 27 is connected to a throttlebody 37 of the air intake system 100. The throttle body 37 includes athrottle valve 39 which rotates to regulate the amount of air flowingthrough the throttle body 37 into the corresponding cylinder of theengine 26. A throttle valve actuator (not shown) is operativelyconnected to the throttle valve 39 to change the position of thethrottle valve 39 and thereby adjust the opening of the throttle valve39 with operation of the throttle lever 86 on the handlebar 84. In thepresent implementation, the throttle valve actuator is a mechanicallinkage, although this is simply one non-limiting implementation. Theposition and the movement of the throttle valve 39 is monitored by athrottle valve position sensor 588 (schematically illustrated in FIG. 8)operatively connected to the throttle valve 39, described in more detailbelow. It is also contemplated that the throttle valve actuator could bein the form of an electric motor. The electric motor could change theposition of the throttle valve 39 based on input signals received froman electronic control module (not shown) which in turn receives inputssignals from a position sensor associated with the throttle lever 86 onthe handlebars 84. Further details regarding such drive-by wire throttlesystems can be found in International Patent Application No.PCT/US2013/048803 filed on Jun. 29, 2013, the entirety of which isincorporated herein by reference.

The engine 26 receives fuel from the fuel tank 28 via Direct Injection(DI) injectors 41 and Multi Point Fuel Injection (MPFI) injectors 45(both shown in at least FIG. 4), having an opening in the cylinders. Thefuel-air mixture in each of the left and right cylinders of the engine26 is ignited by an ignition system including spark plugs 43 (best seenin FIG. 2). Engine output power, torque and engine speed are determinedin part by throttle opening and in part by the ignition timing, and alsoby various characteristics of the fuel-air mixture such as itscomposition, temperature, pressure and the like. Methods of controllingthe fuel-air mixture, according to some implementations of the presenttechnology, will be described in more detail below in reference to FIG.24.

Exhaust gases resulting from the combustion events of the combustionprocess are expelled from the engine 26 via an exhaust system 600 (FIG.5). As shown in FIG. 4, an exhaust outlet 29 is defined in the frontportion of each cylinder of the engine 26. Each exhaust outlet 29 has anexhaust valve 129. The exhaust outlets 29 are fluidly connected to anexhaust manifold 33. The exhaust system 600 includes an exhaust pipe 202which is connected to the exhaust manifold 33 and extends forwardlytherefrom to direct the exhaust gases out of the engine 26.

In the present implementation, the exhaust pipe 202 is a tuned pipewhich has a geometry suitable for improving efficiency of the engine 26.

A turbocharger 300 is operatively connected to the engine 26. Theturbocharger 300 compresses air and feeds it to the engine 26. As shownin FIGS. 6 and 12, the turbocharger 300 has a housing 302 defining anair compressor 310 and an exhaust turbine 350. With additional referenceto FIG. 19, the exhaust turbine 350 includes a turbine inlet 355 with anarea 354, which is defined in turbochargers generally as thecross-sectional area of a volute 352 (measured at the tongue) of theexhaust turbine 350. The air compressor 310 includes a compressor wheeland is part of the air intake system 100. Intake air flowing past therotating compressor wheel is compressed thereby, as described above. Therotation of the compressor wheel is powered by a turbine wheel 351(FIGS. 19, 25) of the exhaust turbine 350, which is part of the exhaustsystem 600. The turbine wheel 351 is rotated about a turbine axis 353(FIG. 19) by exhaust gases expelled from the engine 26 and directed toflow over the blades of the turbine wheel 351. It is contemplated that,in some implementations, the air compressor 310 could be a supercharger,in which the compressor wheel would be directly powered by the engine26. The exhaust system 600 will be described in greater detail below.

Referring to FIGS. 6 and 7, the snowmobile 10 further includes alubrication system to provide lubricating oil to the engine 26 and tothe turbocharger 300. The engine 26 is fluidly connected to an oilreservoir 52 which supplies oil to the crankshaft 126 and the exhaustvalves 129 of the engine 26. The oil reservoir 52 is also fluidlyconnected to the turbocharger 300 to provide lubricating oil thereto.The turbocharger 300 is also fluidly connected to the engine 26, as willbe described further below.

A primary oil pump 54 is fastened to and fluidly connected to the oilreservoir 52. It is contemplated that the pump 54 and the oil reservoir52 could be differently connected together or could be disposedseparately in the snowmobile 10. The primary oil pump 54 pumps oil fromthe reservoir 52 to the engine 26 and the turbocharger 300. The primaryoil pump 54 includes four outlet ports for pumping out oil from the oilreservoir 52. Two outlet ports 53 supply oil to the crankshaft 126.Another outlet port 55 supplies oil to one of the exhaust valves 129.The fourth outlet port 57 supplies oil to the turbocharger 300.Depending on the implementation, it is contemplated that the primary oilpump 54 could include more or fewer outlet ports depending on specificdetails of the implementation.

A secondary oil pump 56 and an oil/vapor separator tank 59 are fluidlyconnected between the turbocharger 300 and the engine 26. The secondaryoil pump 56 receives oil that has passed through the turbocharger 300,and pumps that oil to the other exhaust valve 129. FIG. 7 illustratesthe flow directions of oil from the pumps 54, 56 and through theturbocharger 300 to the engine 26 via schematic diagram. It is furthernoted that in the present implementation, the turbocharger 300 is aball-bearing based turbocharger 300 which is dimensioned for low oilflow lubrication in order to provide efficient responsiveness. It iscontemplated that different types of turbochargers could be used indiffered implementations.

With this configuration, only one oil reservoir 52 is utilized forlubricating both the turbocharger 300 and the engine 26. It iscontemplated that the snowmobile 10 could also be arranged such that thesecondary oil pump 56 could be omitted. It is also contemplated that oilcould be circulated to the crankshaft 126, rather than the exhaustvalves 129, after having passed through the turbocharger 300.

With additional reference to FIGS. 8 to 19, the exhaust system 600 willnow be described in further detail. The exhaust gas expelled from theengine 26 flows through the exhaust outlets 29, through the exhaustmanifold 33, and into the exhaust pipe 202, as is mentioned above. Theexhaust pipe 202, which as mentioned above is a tuned pipe 202, iscurved and has a varying diameter along its length. Other types ofexhaust pipes 202 are contemplated. As shown in FIG. 5, the exhaust pipe202 includes a pipe inlet 203 fluidly connected to the exhaust manifold33 and a pipe outlet 206 located at the end of the exhaust pipe 202. Theexhaust pipe 202 further has a divergent portion 605 adjacent the pipeinlet 203 and a convergent portion 607 adjacent the pipe outlet 206. Thepipe outlet 206 is positioned downstream from the pipe inlet 203. It iswell known in the art of two stroke engines that the goal of theconverging-diverging type tuned pipe is to have the diverging sectioncreate a returning rarefaction wave and the converging section create areturning pressure wave which pushes any excess fresh air-fuel mixturewhich flowed out of the cylinder into the exhaust pipe, back into thecylinder. Pushing the fresh mixture back into the cylinder is desiredsince this allows the returning pressure wave to “super charge” thecylinder giving it more fresh mixture than if the cylinder was filled atambient pressure. The nomenclature “tuned pipe” is used because thedimensions of the pipe are specifically chosen so this super chargingoccurs within the pipe at a particular value of one or more parameters,or range of values thereof such as at a particular temperature and/orpressure, which coincide with a desired operating RPM or desiredoperating RPM range of the engine. Once the physical dimensions of thetuned pipe are selected, the super charging actions of that pipe will beoptimal at the specific parameter values for which it was tuned andbecause conventional tuned pipes are fixed in dimension, theseparameters are not adjustable during use of the vehicle in which theengine is installed. When the tuned pipe is not operating at thesespecific tuned parameter values, the super charging effect will be lessthan optimal and consequently the operation of the engine will be lessthan optimal at the desired operating RPM. For this reason, when therestrictions of a turbocharger or a variable valve such as the valve 630are added along the flow path of the exhaust which causes thetemperature and/or pressure to be changed within the tuned pipe at anygiven time of operation, compensations must be made in order to preventthese changes from negatively affecting engine performance or otherwiselimit negative effects on engine performance. It should thus beunderstood that two stroke engines, due to this super charging action,are sensitive to variations within the tuned pipe.

The exhaust system 600 also includes a bypass conduit 620 to direct theflow of the exhaust gas to either bypass the turbocharger 300 or to passthrough the exhaust turbine 350 of the turbocharger 300 to operate theair compressor 310. The pipe outlet 206 located at the end of theexhaust pipe 202 fluidly communicates with the bypass conduit 620.Specifically, the bypass conduit 620 defines an exhaust inlet 622 whichis fluidly connected to the pipe outlet 206. The exhaust inlet 622 andthe pipe outlet 206 are arranged such that exhaust gas passing from thepipe outlet 206 into the exhaust inlet 622 passes through the inlet 622generally normal to the inlet 622. A central axis 629 (FIGS. 13, 14) ofthe exhaust inlet 622 illustrates the general direction of exhaust gasflow into the bypass conduit 620. In the present implementation, thecentral axis 629 coincides with the center of the circular inlet 622,but that may not always be the case.

The bypass conduit 620 is further fluidly connected to the housing 302of the turbocharger 300. More specifically, the bypass conduit 620 ismechanically connected to the turbocharger housing 302 in the presentimplementation by a clamp 303. It is contemplated that the bypassconduit 620 could be an independent apparatus from the turbocharger 300.It is also contemplated that the bypass conduit 620 could be fastened orotherwise mechanically connected to the turbocharger housing 302. It isfurther contemplated that the bypass conduit 620 and the turbochargerhousing 302 could be integrally formed.

The bypass conduit 620 is generally Y-shaped, with an inlet conduitportion 690 extending from the exhaust inlet 622 and branching into twooutlet conduit portions 692, 694 (FIG. 14). As such and as is mentionedabove, the bypass conduit 620 serves to selectively direct the exhaustgas which enters through the exhaust inlet 622 either into the exhaustturbine 350 or bypassing the exhaust turbine 350. As shown in FIG. 14,the turbine outlet portion 692 of the bypass conduit 620 (one branch ofthe Y-shape) defines a passage ending in an outlet 615 that fluidlycommunicates with the turbine inlet 355. A bypass outlet portion 694(the other branch of the Y-shape) allows exhaust gas to bypass theturbocharger 300 to exit the bypass conduit 620 through a bypass outlet626. The bypass outlet portion 694 defines a passage 625 which allowsfor fluid communication between the exhaust inlet 622 and the outlet626. The outlet 626 and the passage 625 can be seen in FIG. 17. Bestseen in FIG. 16, the bypass conduit 620 further includes a flow divider628 disposed between the conduit portions 692, 694. The flow divider 628aids in smoothly dividing the exhaust gas flow through the bypassconduit 620, in order to aid in avoiding flow separation or the creationof vortices in the exhaust gas flow. To that end, the flow divider 628is generally shaped and arranged to avoid abrupt edges.

Flow of the exhaust gas through the passage 625 is selectivelycontrolled by a valve 630 disposed in the bypass conduit 620, inconjunction with a system controller 500 controlling the valve 630. Morespecifically, the valve 630 is a valve for selectively diverting exhaustgas away from the turbocharger 300. In the present implementation, thevalve 630 is disposed in the passage 625, and more specifically at avalve seat 623 thereof. It is contemplated that the valve 630 could bedisposed elsewhere in the bypass conduit 620, for example nearer theexhaust inlet 622 and just upstream from the passage 625, depending onthe specific implementation of the valve 630. It is also contemplatedthat in some implementations, the valve 630 could selectively open orclose the turbine outlet portion 692 rather than the bypass passage 625.

With reference to FIGS. 26 to 29, the valve 630 has a base portion 400and a body portion 402 extending from the base portion 400. The baseportion 400 is configured for pivotably mounting the valve 630 withinthe bypass conduit 620 and thus defines a valve pivot axis 404 aboutwhich the valve 630 is pivotable during use. More specifically, the baseportion 400 is generally cylindrical and has an axle 440 including twoaxle portions 441 extending in opposite directions from a centralsection of the base portion 400. While the axle 440 is made integrallywith the valve 630 in this embodiment, it is contemplated that, in otherembodiments, the axle 440 could be a separate component (e.g., twoseparate axle portions connectable to the base portion 400).

The body portion 402 is the portion of the valve 630 which is used toblock the passage 625. The body portion 402 has an upstream side 406 anda downstream side 408 opposite the upstream side 406. The upstream side406 is exposed, during use, to fluid flow in the bypass conduit 620. Inother words, the upstream side 406 generally faces the inlet 622 whilethe downstream side 408 faces the bypass outlet 626. The body portion402 of the valve 630 is shaped to facilitate control of exhaust gas flowthrough the passage 625. Notably, the body portion 402 has a generallypointed shape defining a rounded tip 410 at a location of the bodyportion 402 furthest from the base portion 400 in a length direction ofthe valve 630 (generally perpendicular to the valve pivot axis 404). Assuch, the body portion 402 of the valve 630 (i.e., the portion of thevalve 630 used to block the passage 625) can be said to be generallyelongated.

A periphery 412 of the body portion 402 generally defines the shapethereof. The periphery 412 includes two opposite lengthwise edges 414that extend from the base portion 400 in a direction generally parallelto the length direction of the valve 630. The periphery 412 alsoincludes a rounded edge 416 defined by the rounded tip 410, and twoconverging angular edges 418 extending between the two lengthwise edges414 and respective ends of the rounded edge 416 (i.e., the angular edges418 connect the lengthwise edges 414 to the rounded edge 416). Theangular edges 418 converge toward each other as the two angular edges418 extend from the two lengthwise edges 414 to the ends of the roundededge 416. Each of the angular edges 418 is thus disposed at an angle θrelative to the length direction of the valve 630. The angle θ may bebetween 10° and 45° inclusively. For instance, in this implementation,the angle θ is approximately 30°.

As shown in FIG. 26, the body portion 402 of the valve 630 is generallysymmetrical about a plane of symmetry PS bisecting the rounded tip 410.The plane of symmetry PS is perpendicular to the valve pivot axis 404.One of each of the lengthwise edges 414 and angular edges 418 isdisposed on either side of the plane of symmetry PS. Moreover, in thisimplementation, the base portion 402 of the valve 630 is alsosymmetrical about the plane of symmetry PS. However, it is contemplatedthat the valve 630 could not be symmetrical about the plane PS.

A width of the body portion 402, measured in a direction parallel to thevalve pivot axis 404, varies along the length direction of the valve630. For instance, the width of the body portion 402 is largest adjacentthe base portion 400. More specifically, a maximal width W_(max) of thebody portion 402 is measured between the two opposite lengthwise edges414. The width of the body portion 402 decreases at the angular edges418 along the length direction of the valve 630 toward the rounded tip410. Notably, the width of the body portion 402 is smallest at therounded tip 410.

As shown in FIG. 27, a length L_(V) of the valve 630 is measured fromthe base portion 400 to the rounded tip 410 in the length direction ofthe valve 630. In this implementation, the length L_(V) of the valve 630is greater than or equal to the maximal width W_(max) of the bodyportion 402. Notably, the length L_(V) is greater than the maximal widthW_(max) such that a ratio L_(V)/W_(max) of the length L_(V) of the valve630 over the maximal width W_(max) of the body portion 402 is greaterthan 1. For instance, the ratio L_(V)/W_(max) may be between 1 and 2inclusively. Notably, the ratio L_(V)/W_(max) is between 1.2 and 1.6. Inone particular embodiment, the ratio L_(V)/W_(max) is approximately 1.3.

Furthermore, a ratio W_(max)/R_(T) of the maximal width W_(max) of thebody portion 402 over a tip radius R_(T) of the rounded tip 410 isgreater than 2. For instance, the ratio W_(max)/R_(T) may be between 2and 6 exclusively. In this implementation, the ratio W_(max)/R_(T) isapproximately 3.

As shown in FIG. 26, the body portion 402 of the valve 630 has a ridge420 disposed on the upstream side 406. Notably, the ridge 420 protrudesfrom a generally planar surface 422 of the upstream side 406. In thisimplementation, a height of the ridge 420 measured from the surface 422is constant. The ridge 420 forms a closed shape which, in thisimplementation, is generally pentagonal. As will be described in moredetail below, the periphery 412 contours part of the ridge 420.

In this implementation, the ridge 420 has five edges including a baseedge 424, two outwardly-extending edges 426 and two inwardly-extendingedges 428. The base edge 424 extends generally parallel to the valvepivot axis 404 and is disposed near the base portion 400 of the valve630. Each outwardly-extending edge 426 extends from a corresponding endof the base edge 424 outwardly toward a corresponding one of thelengthwise edges 414 of the periphery 412 of the body portion 402. Theinwardly-extending edges 428 are generally parallel to correspondingones of the angular edges 418 of the periphery 412 of the body portion402. Each inwardly-extending edge 428 extends from an end of acorresponding one of the outwardly-extending edges 426.

The edges 424, 426, 428 of the ridge 420 meet at corresponding roundedvertices 430 ₁-430 ₅. Notably, the inwardly-extending edges 428 convergeat a distal rounded vertex 430 ₅ which, amongst the vertices 430 ₁-430₅, is furthest from the base portion 400. The distal rounded vertex 430₅ is generally concentric with the rounded edge 416 of the periphery 412of the body portion 402. Notably, the rounded edge 416 of the periphery412 contours the rounded vertex 430 ₅ of the ridge 420. Furthermore, theangular edges 418 and the lengthwise edges 414 contour the inwardly andoutwardly-extending edges 428, 426 respectively.

As shown in FIG. 29, a cross-sectional profile of the ridge 420, whichcan be observed for example along a plane normal to the length directionof the valve 630, is generally trapezoidal.

With reference to FIGS. 27 to 29, the body portion 402 of the valve 630also has a peripheral lip 432 protruding on the downstream side 408 ofthe body portion 402. The peripheral lip 432 extends from the periphery412 of the body portion 402. The peripheral lip 432 therefore hasgenerally the same shape as that defined by the periphery 412. Theperipheral lip 432 has a variable height measured from a surface 434 ofthe downstream side 408 of the body portion 402. The height of theperipheral lip 432 adjacent the base portion 400 is greater than theheight of the ridge 420.

The valve 630 as described above is generally shaped to avoid abruptedges to aid in preventing flow separation or the creation of vorticesin the exhaust gas flow within the bypass conduit 620.

In this implementation, the valve 630 is a single-piece component inthat the base portion 400 and the body portion 402 are made integrally.However, it is contemplated that, in alternative implementations, thebase portion 400 and the body portion 402 may be made as separatecomponents and connected to one another to form the valve 630.

With reference to FIG. 12, an actuator 635 is operatively connected tothe valve 630 to cause the valve 630 to pivot about the valve pivot axis404 (shown in FIG. 26). In this implementation, the actuator 635 is aservomotor. It is contemplated that any other suitable type of actuatormay be used in other implementations. The actuator 635 is connected tothe valve 630 via a linkage assembly 636. More specifically, in thisimplementation, the linkage assembly 636 includes three arms 637, 638,639. The arm 637 is connected to the actuator 635 and is rotatablethereby. The arm 638 is connected to the axle 440 of the base portion400 of the valve 630. The arm 639 is connected between the arms 637,638. Rotation of the arm 637 therefore actuates the two other arms 638,639 and causes the valve 630 to pivot between an open position, a closedposition, and intermediate positions as will be described below. It iscontemplated that, in some implementations, the valve 630 could rotate,translate, or be moved otherwise to control exhaust gas flow through thepassage 625.

The valve 630 is controlled to regulate the flow of exhaust gas throughthe turbocharger 300 by selectively blocking or opening a valve opening627 (FIG. 15) defined by the valve seat 623 of the passage 625. Thevalve opening 627 defined by the valve seat 623 is thus shaped such thatit corresponds to the shape of the body portion 402 of the valve 630(i.e., generally elongated and having a rounded tip). The valve 630 ispivotably mounted at the valve seat 623 via the base portion 400 of thevalve 630 and is selectively movable between: an open position in whichexhaust gas flow through the valve opening 627 (and thus the passage625) is substantially unimpeded by the valve 630; a closed position inwhich the valve 630 fully closes the valve opening 627 such that exhaustgas flow through the valve opening 627 is cut-off by the valve 630; andany number of intermediate positions between the open and closedpositions. In this implementation, as shown in FIG. 15, in its openposition, the valve 630 is at approximately 45° (measured from the valveseat 623—i.e., 0° corresponding to the closed position of the valve630). Moreover, in the open position, the valve 630 contacts a wall ofthe bypass conduit 620 on a side opposite the flow divider 628, but thismay not be the case in all implementations.

A cross-section of the bypass conduit 620 is illustrated in FIGS. 14 to16 to show the different positions of the valve 630. FIG. 14 illustratesthe closed position; FIG. 15 illustrates the open position (alsoillustrated in FIG. 25); and FIG. 16 illustrates one of the manypossible intermediate positions of the valve 630. As can be seen, thevalve 630 is oriented in the bypass conduit 620 such that the roundedtip 410 is downstream of the base portion 400. That is, in the open,closed and intermediate positions, the rounded tip 410 of the valve 630is downstream of the base portion 400. The exhaust gas flow through thebypass conduit 620 for each of the relative positions of the valve 630will be described in more detail below. As can be seen in FIG. 14, inits closed position, the valve 630 contacts the valve seat 623. Morespecifically, in the closed position, the ridge 420 of the body portion402 of the valve 630 sits against the valve seat 623.

In relation to a circular valve, the generally elongated shape of thevalve 630 as described above establishes a more linear relationshipbetween the mass flow of exhaust gas through the opening 627 and theangle at which the valve 630 is open. In other words, a greater controlof the mass flow of exhaust gas through the opening 627 is made possibleby the shape of the valve 630. Consequently, back pressure within theexhaust system 600 caused by opening the valve 630 can be controlledmore precisely than with a circular valve. This can be seen in the chartof FIG. 30 which illustrates a percentage mass flow through an openingas a function of a position of a valve (expressed as a percentage—0%corresponding to the closed position of the valve; 100% corresponding tothe fully open position of the valve) for the valve 630 of the presenttechnology and for a circular valve. The percentage mass flow reaches100% when the valve is in the open position (for the valve 630 thiscorresponds to a 45° angle, but is approximately 90° for the circularvalve). Notably, the performance curve P1 represents the percentage massflow through the opening 627 as a function of the position of the valve630 in accordance with the present technology. By way of contrast, theperformance curve PA represents the percentage mass flow through acircular opening as a function of the position of its correspondingcircular valve. As can be seen, in accordance with the presenttechnology, the relationship between the mass flow percentage throughthe opening 627 and the position of the valve 630 is markedly morelinear than for the circular valve, particularly at smaller angles ofthe valve (e.g., below 45%—i.e., below 20° for the valve 630).

In addition to the particular shape of the valve 630, the differentpassages defined by the bypass conduit 620 are also oriented in aparticular manner. For instance, with reference to FIG. 14, in thisembodiment, the bypass outlet 626 of the bypass outlet portion 694 andthe outlet 615 of the turbine outlet portion 692 face directions thatare not parallel to one another. In particular, an angle ψ is formedbetween a plane 657 extending through the outermost face of the bypassoutlet portion 694 that defines the bypass outlet 626 and a plane 659extending through the outermost face of the turbine outlet portion 692that defines the outlet 615. The angle ψ formed between the planes 657,659 measures between 40° and 80° inclusively. More specifically, in thisembodiment, the angle ψ measures approximately 60°.

Furthermore, with continued reference to FIG. 14, an angle β formedbetween a plane 661 extending through the periphery of the valve seat623 that defines the opening 627 and the central axis 629 of the exhaustinlet 622 measures between 0° and 40° inclusively. In particular, inthis embodiment, the angle β measures approximately 20°. An angle αformed between an axis 655 normal to the plane 661 and the central axis629 of the exhaust inlet 622 measures between 100° and 140° inclusively.In particular, in this embodiment, the angle α measures approximately115°. An angle γ formed between the central axis 629 of the exhaustinlet 622 and an axis 651 normal to the plane 657 extending through theoutermost face of the bypass outlet portion 694 that defines the bypassoutlet 626 measures between 0° and 40° inclusively. In particular, inthis embodiment, the angle γ measures approximately 20°. Lastly, anangle ϕ formed between the plane 657 extending through the outermostface of the bypass outlet portion 694 that defines the bypass outlet 626and an axis 653 normal to the plane 659 extending through the outermostface of the turbine outlet portion 692 that defines the outlet 615measures between 10° and 50° inclusively. In particular, in thisembodiment, the angle 4 measures approximately 30°. It is to beunderstood that, in this embodiment, the axis 653 is parallel to theturbine axis 353 about which the turbine wheel 351 rotates. Inparticular, the axis 653 is coaxial with the turbine axis 353.

The exhaust system 600 further includes the system controller 500, whichis operatively connected to an engine control unit (or ECU) and/or theelectrical system (not shown) of the snowmobile 10. The engine controlunit is in turn operatively connected to the engine 26. As will bedescribed in more detail below, the system controller 500 is alsooperatively and communicatively connected to an atmospheric pressuresensor 504, also referred to as an air intake sensor 504, for sensingthe atmospheric or ambient air pressure of the intake air coming intothe air intake system 100. It should be noted that the atmosphericpressure sensor 504, also referred to herein as an intake pressuressensor 504, senses the air pressure in the primary airbox 120, and assuch measures the air intake pressure from air entering either from theambient air around the snowmobile 10 and/or the air entering the primaryairbox 120 from the turbocharger 300.

Similarly, the system controller 500 is also operatively andcommunicatively connected to an atmospheric temperature sensor 505 (FIG.5), also referred to as an air intake temperature sensor 505, forsensing the atmospheric or ambient air temperature of the intake aircoming into the air intake system 100. It should be noted that theatmospheric temperature sensor 505 senses the air temperature in theprimary airbox 120, and as such measures the air intake temperature fromair entering either from the ambient air around the snowmobile 10 and/orthe air entering the primary airbox 120 from the turbocharger 300.

The actuator 635 for selectively moving the valve 630 is communicativelyconnected to the system controller 500 such that the position of thevalve 630 is controllable thereby. It is contemplated that the valve 630could be differently controlled or moved, depending on theimplementation.

As is illustrated in the schematic diagram of FIG. 8 and as will bedescribed in more detail below, the system controller 500 is alsooperatively connected to the throttle valve position sensor 588 fordetermining the position of the throttle valve 39, a rate of opening ofthe throttle valve 39, or both. In some modes of operation of theexhaust system 600, the valve 630 is selectively moved based on thethrottle valve position determined by the throttle valve position sensor588. In some modes of operation of the exhaust system 600, the valve 630is selectively moved based on the rate of change of the throttle valveposition or the rate of opening of the throttle valve 39, as determinedby the throttle valve position sensor 588.

As is illustrated schematically in FIG. 8 and as will also be describedin more detail below, the system controller 500 is further connected toan exhaust pressure sensor 590 for sensing the pressure at a point alongan exhaust path of the engine 26, near the exhaust outlets 29. Thepressure sensed by the exhaust pressure sensor 590 is used to determinethe back pressure of the engine 26. Back pressure is understood to bethe resistance to the flow of the exhaust gas between the engine 26 andan outlet of the muffler 650 due, at least in part, to twists, bends,obstacles, turns and sharp edges present in the various components ofthe exhaust system 600. In the present technology, reducing backpressure can assist in optimizing performance of the engine 26, as highback pressure can negatively impact the efficiency of the engineperformance. Reducing the amount of back pressure in the exhaust system600 may also have the effect of reducing what is known as “turbo lag”,which is a delay in the response of a turbocharged engine after thethrottle lever 86 has been moved for operating the throttle system.

Furthermore, in order to ensure good scavenging within the cylinders ofthe engine 26, in this embodiment, a ratio of the exhaust pressure overthe intake pressure (as measured by the sensors 590, 504 respectively)is kept relatively constant. Notably, in this embodiment, the ratio ofthe exhaust pressure over the intake pressure is maintained between 1.1and

With reference to FIG. 5, in the present implementation, the exhaustpressure sensor 590 is configured to sense the pressure along theexhaust path of the engine 26. In particular, the exhaust pressuresensor 590 has a sensing port (not shown) which is fluidly connected tothe exhaust pipe 202. In the present implementation, the exhaustpressure sensor 590 senses a pressure within the diverging portion 605of the exhaust pipe 202 but it is contemplated that the exhaust pressuresensor 590 could be configured so as to sense a pressure along otherareas of the exhaust pipe 202. The sensing port of the exhaust pressuresensor 590 is connected via intermediate tube members to the exhaustpipe 202 since the exhaust pressure sensor 590 is not designed towithstand the elevated temperatures within the exhaust pipe 202.Notably, a metallic tube 593 is fluidly connected to the exhaust pipe202, and a rubber tube 591 is in turn fluidly connected between themetallic tube 593 and the sensing port of the exhaust pressure sensor590. The lengths and diameters of the tubes 591, 593 are chosen so thatpressure waves travelling through the exhaust pipe 202 are notsignificantly distorted when they arrive at the sensing port of theexhaust pressure sensor 590, thus ensuring greater accuracy of thepressure sensed by the exhaust pressure sensor 590. It is contemplatedthat the exhaust pressure sensor 590 could be differently arranged,depending on details of a particular implementation. In someimplementations, the system 600 could further include a differentialsensor for determining a pressure differential between the air intakepressure entering the engine 26 and the exhaust pressure of exhaust gasexiting the engine 26. It is also contemplated that the differentialsensor could replace one or both of the intake pressure sensor 504 andthe exhaust pressure sensor 590 in some implementations.

As is also illustrated in FIG. 8, the system controller 500 is furtherconnected to several sensors for monitoring various exhaust systemcomponents. The system controller 500 is communicatively connected to anexhaust pipe temperature sensor 512 to detect the temperature of theexhaust pipe 202. As can be seen in FIG. 5, the exhaust pipe temperaturesensor 512 includes a temperature probe connected to an outer wall ofthe exhaust pipe 202 within the converging section 607, but otherpositions along the exhaust pipe 202 are contemplated. The temperatureprobe extends within the exhaust pipe 202 so as to measure thetemperature of the exhaust gas circulating therein. The systemcontroller 500 is also communicatively connected to an exhaust oxygensensor 513 to detect a concentration of oxygen in the exhaust transitingthe exhaust pipe 202. As can be seen in FIG. 5, the exhaust oxygensensor 513 includes a probe connected to and extending through the outerwall of the exhaust pipe 202 within the converging section 607, butother positions along the exhaust pipe 202 are contemplated.

Similarly, the system controller 500 is communicatively connected to amuffler temperature sensor 550 to detect the temperature of the muffler650. These sensors 512, 550 could be used to monitor possibleoverheating or temperature imbalances, as well as to provide informationto the system controller 500 to use in control methods such as thosedescribed herein. In order to determine an engine speed of the engine26, the system controller 500 is further communicatively connected to anengine sensor 586 disposed in communication with the engine 26.

The exhaust system 600 further includes an exhaust collector 640 fluidlyconnected to the bypass conduit 620 and the turbocharger 300. Theexhaust collector 640, shown in isolation in FIGS. 20A to 20C, includesan inlet 642 through which the exhaust collector 640 receives exhaustgas from both the bypass conduit 620 and the exhaust turbine 350.

More specifically, the inlet 642 receives exhaust gas that bypasses theexhaust turbine 350 and exits through the outlet 626 of the bypassconduit 620. The inlet 642 also receives exhaust gas that has passedthrough the exhaust turbine 350 from an outlet 315 of the turbochargerhousing 302. The inlet 642 includes two portions: a lower portion 643and an upper portion 645. The lower and upper portions 643, 645 areintegrally connected to define a peanut-shaped opening in the inlet 642.It is contemplated that the inlet 642 could be differently shapeddepending on the implementation.

The lower portion 643 is fluidly connected to the housing 302 to receiveexhaust gas therethrough from the exhaust turbine 350 through the outlet315. The upper portion 645 is fluidly connected to the bypass conduitoutlet 626 to receive therethrough the exhaust gas that has bypassed theexhaust turbine 350. The exhaust collector 640 also includes an outlet646, through which exhaust gas passing into the exhaust collector 640exits. It is contemplated that the two inlet portions 643, 645 could beseparated in some implementations, such that the exhaust collector 640could be generally Y-shaped for example.

The exhaust collector 640 is bolted to the housing 302 and the bypassconduit 620 using through-holes 641 defined in a periphery of the inlet642. It is contemplated that the exhaust collector 640 could bedifferently connected to the turbocharger housing 302 and the bypassconduit 640 in different implementations. It is also contemplated thatthe exhaust collector 640 could be integrally formed with the bypassconduit 620 and/or the turbocharger housing 302.

With reference to FIG. 10, the exhaust system 600 includes a muffler650. The muffler 650 includes one muffler inlet 654 through which toreceive exhaust gas from the exhaust system 600. The muffler 650 isfluidly connected to the collector outlet 646 of the exhaust collector640. The muffler inlet 654 and the collector outlet 646 are held inplace by springs as can be seen in the Figures. It is contemplated thatdifferent methods could be employed to connect the muffler 650 to theexhaust collector 640. As can be seen in the Figures, the muffler 650includes only the single inlet 654 for receiving exhaust gas bothbypassing and passing through the exhaust turbine 350.

Flow of the exhaust gas through the exhaust system 600, specificallybetween the exhaust pipe 202 and the muffler 650, will now be describedin more detail. As is described briefly above, the valve 630 in thebypass conduit 620 selectively controls the flow of exhaust gas eitherinto the exhaust turbine 350 or bypassing the exhaust turbine 350 bysending the exhaust gas out through the conduit outlet portions 692,694.

In the present technology, the bypass conduit 620 is designed andarranged to balance two competing interests: the first being to allowfor efficient exhaust gas flow when bypassing the turbocharger 300 inorder to operate the engine 26 as a naturally aspirated engine 26, andthe second being not impeding efficient operation of the turbocharger300 when desired. In traditional turbo-charged engines, all exhaust gaswould be directed to the turbocharger 300, with an associated bypassonly being used in the case of too much exhaust gas flow into theturbocharger. In the present technology, exhaust gas can be directedeither to bypass the turbocharger 300 for naturally aspirated operationor into the turbocharger 300 for turbo-charged operation. The inclusionof the intake bypass valve 123 further aids in allowing for naturallyaspirated operation or turbo-charged operation of the engine 26. As isdescribed above, the intake bypass valve 123 allows for atmospheric orambient airflow into the primary airbox 120 when the pressure in theprimary airbox 120 falls below a threshold, due the turbocharger 300 notoperating or spooling up and thus not providing sufficient compressedair to the primary airbox 120. By including both the valve 630 and thebypass valve 123, each of which are independently operated, both airintake and exhaust gas are managed to allow for naturally aspirated orturbo-charged operation of the engine 26.

As is mentioned above, exhaust gas entering the bypass conduit 620 flowsgenerally parallel to the central axis 629 of the inlet 622. As can beseen in FIGS. 13 to 16, the central axis 629, and thus the center of theflow of exhaust gas, is directed to the turbine outlet portion 692 sideof the flow divider 628. As the flow divider 628 is situated toward thebypass side with respect to the central axis 629, it should beunderstood that more than half of the exhaust gas flow is thereforeinitially directed toward the turbine outlet portion 692.

On the bypass outlet portion 694 side of the central axis 629 (to theleft of the axis 629 in the Figures), it can also be seen that some ofthe exhaust gas flow, parallel to the central axis 629, is directedtoward the opening 627. As the conduit inlet 622 and opening 627 of thepassage 625 are at least partially aligned along the direction of thecentral axis 629, at least a portion of the exhaust gas entering theconduit inlet 622 parallel to the flow axis flows unobstructed into thebypass passage 625 when the valve 630 is in the open position. As theengine 26 is intended to be naturally aspirated in standard operation,at least a portion of exhaust gas flowing generally directly through thebypass conduit 620 and into the exhaust collector 640, with a minimum ofturns, bends, etc. further assists in decreasing back pressure, again inthe aims of optimizing engine performance.

It should be noted that, as will be described further below, thepercentage of exhaust gas flow directed toward each of the outputconduits 692, 694 does not necessarily correspond to the percentage ofexhaust gas that flows therethrough.

The two different flow patterns of exhaust gas entering the bypassconduit 620 will now be described in reference to flow paths 670, 675schematically illustrated in FIG. 8. Depending on the position of thevalve 630, the exhaust gas can flow along a bypass exhaust flow path670, a turbine exhaust flow path 675, or a combination of the two paths670, 675.

Exhaust gas flowing along the bypass exhaust flow path 670 passesthrough the passage 625, which is not blocked by the valve 630 when thevalve 630 is in the open position. The bypass exhaust flow path 670 isdefined from the exhaust inlet 622 of the bypass conduit 620 to theexhaust collector 640. Exhaust gas flowing along the bypass exhaust flowpath 670 passes through the exhaust inlet 622, then through the bypassconduit 620, and then into the exhaust collector 640. Specifically,exhaust gas flowing along the bypass exhaust flow path 670 is receivedin the upper portion 645 of the inlet 642.

The turbine exhaust flow path 675 is similarly defined from the exhaustinlet 622 of the bypass conduit 620 to the exhaust collector 640.Exhaust gas flowing along the second exhaust flow path passes throughthe exhaust inlet 622, then through the turbine outlet portion 692 ofthe bypass conduit 620, then through the exhaust turbine 350, and theninto the exhaust collector 640. Specifically, exhaust gas flowing alongthe turbine exhaust flow path 675 is received in the lower portion 643of the inlet 642.

For each flow path 670, 675, exhaust gas passes out of the collectoroutlet 646 and into the muffler inlet 654. The single muffler inlet 654of the muffler 650 receives the exhaust gas from both the bypass exhaustflow path 670 and turbine exhaust flow path 675.

Even though the majority of exhaust gas flow is oriented toward theturbine outlet portion 692, a majority of the exhaust gas entering theexhaust inlet 622 flows along the bypass exhaust flow path 670, throughthe bypass outlet portion 694, when the valve 630 is in the openposition. The flow path 675 through the exhaust turbine 350, designed toturn under pressure from exhaust gas flowing therethrough, is morerestrictive and causes more back pressure than the flow path 670 throughthe bypass passage 625. More of the exhaust gas is therefore directedthrough the passage 625, even if the initial flow direction is towardthe turbine outlet portion 692. It should be noted that a portion of theexhaust gas entering the bypass conduit 620 will still flow through theexhaust turbine 350 even when the valve 630 is fully open.

When the valve 630 is in the closed position, a majority (generally all)of the exhaust gas entering the exhaust inlet 622 flows along theturbine exhaust flow path 675. As is illustrated schematically, exhaustgas flowing along the turbine exhaust flow path 675 is deflected by thevalve 630, as the valve 630 blocks the passage 625 in the closedposition. As some of the exhaust gas entering through the conduit inlet622 flows in parallel to the central axis 629, at least a portion of thevalve 630 is contacted by, and diverts, exhaust gas entering the inlet622.

As is mentioned above, the valve 630 can also be arranged in anintermediate position, such as that illustrated in FIG. 16 (just as onenon-limiting example). With the valve 630 in the intermediate position,a portion of the exhaust gas is allowed through the passage 625 tobypass the exhaust turbine 350 and a portion of the exhaust gas isdeflected through the turbine outlet portion 692 toward the exhaustturbine 350. In the intermediate position, at least a portion of thevalve 630 is contacted by the exhaust gas entering through the conduitinlet 622 and flowing parallel to the axis 629.

The exhaust gas thus flows along both of the bypass exhaust flow path670 and the turbine exhaust flow path 675 when the valve 630 is in oneof the intermediate positions. The ratio of the portion of exhaust gasflowing along the bypass exhaust flow path 670 to the portion of exhaustgas flowing along the turbine exhaust flow path 675 depends on variousfactors, including at least the angle at which the valve 630 isarranged. Generally, the closer the valve 630 is to the open position,the more exhaust gas will flow along the bypass exhaust flow path 670and vice versa.

As will be described in more detail below, the valve 630 is used tomanage exhaust gas flow through the flow paths 670, 675. For example, insome scenarios, the valve 630 is selectively moved to the closedposition (or toward the closed position) when the engine 26 is operatedbelow a threshold atmospheric pressure. In such a scenario, theturbocharger 300 could be used to help boost engine performance when thesnowmobile 10 climbs in altitude, where the air is thinner and as suchless oxygen will enter the engine 26 (having a detrimental effect onperformance).

Regardless of the position of the valve 630, in this implementation,there is no physical barrier blocking air flow between the exhaust inlet622 and the turbine inlet 355. As is mentioned above, a portion of theexhaust gas entering through the bypass inlet 622 passes through theturbine outlet portion 692 and enters the exhaust turbine 350 throughthe turbine inlet 355, even when the valve 630 is in the open position.The relatively small portion of exhaust gas entering the exhaust turbine350 aids in creating a pressure difference between positions upstreamfrom the exhaust turbine 350 and downstream therefrom. This pressuredifference generally improves the responsiveness of the turbocharger300, generally making the exhaust turbine 350 spool up more rapidly andassisting in decreasing the turbo lag.

Similarly, there is no physical barrier closing the turbine outlet 315when the exhaust gas flows along the bypass exhaust flow path 670. Assuch, flow of exhaust gas out of the bypass outlet 626 causes an airpressure reduction in the turbine outlet 315. This low pressure zonealso assists in decreasing the turbo lag and in increasing the spool upspeed. It is also noted that there is also no barrier closing the bypassoutlet 626 when the exhaust gas is directed to the turbine exhaust flowpath 675 and flowing out of the turbine outlet 315.

The exhaust system 600, according to the present technology and asdescribed above, is generally intended to be operated as a naturallyaspirated engine system, with the exhaust gas generally bypassing theexhaust turbine 350, other than in specific scenarios where additionalboost from the turbocharger 300 is necessitated. This is in contrast tosome standard turbo-charged engine arrangements, where a turbocharger isused in standard operation and a turbocharger bypass is used to preventoverload of the compressor.

In the arrangement and alignment of the exhaust system 600 of thepresent technology, in contrast to conventional turbochargerarrangements, a majority of the exhaust gas flows through the passage625 when the valve 630 is in the open position (described above).Exhaust gas flow, especially to allow the gas to bypass the turbocharger300 without creating excessive back pressure, is further managed by thecomparative cross-sections of the two flow paths 670, 675. Specifically,in the present technology, the area of the opening 627 of the passage625 (for the bypassing flow path 670) and the intake area 354 of theexhaust turbine 350 (in the turbine flow path 675) are of similardimensions.

The arrangement of the relative areas of the openings 627, 355 in thetwo flow paths 670, 675 allows exhaust gas to both bypass the exhaustturbine 350 without creating excessive back pressure (which can bedetrimental to operation of the engine 26) while still allowing goodexhaust gas flow through the turbine inlet 355 when the turbine 300 issolicited. According to the present technology, the area of the opening627 is generally between 0.75 and 1.25 times the area 354 of theturbocharger inlet 355. In the present implementation, the area 354 ofthe turbocharger inlet 355 is slightly greater than the area of theopening 627. It is contemplated, however, that the area of the opening627 could be greater than the area 354 of the turbocharger inlet 355 insome implementations.

In further contrast to conventional turbocharger arrangements, thebypass outlet 626 has been specifically arranged such that there is notan excessive amount of deviation of the exhaust flow necessary for theflow to travel from the bypass conduit inlet 622 to the bypass outlet626. A normal of the bypass outlet 626 is at an angle of about 20degrees to the central axis 629 in the present implementation (althoughthe exact angle could vary). With this arrangement, a portion of theexhaust gas entering the inlet 622, illustrated between lines 601 and603 in FIG. 15, both parallel to the central axis 620, will passdirectly through the bypass conduit 620, meaning through the passage 625and the opening 627, and out of the bypass outlet 626 without deviating.This is true even for a plurality of positions of the valve 630 betweenthe fully open and fully closed positions.

When the snowmobile 10 is not being operated below a thresholdatmospheric pressure, the exhaust system 600 will tend to send exhaustgas along the bypass exhaust flow path 670 bypassing the exhaust turbine350 and the engine 26 will operate as a naturally aspirated engine 26.When the snowmobile 10 is operated below such a threshold air intakepressure, for example at high altitudes/low atmospheric pressure, thevalve 630 will move toward the closed position (either partially orcompletely) to send some or all of the exhaust gas to the exhaustturbine 350 to provide boost to the engine 26. More details pertainingto operation of the valve 630 with respect to operating conditions willbe provided below.

Example Operation of the Exhaust System

With reference to FIGS. 31 and 32, one non-limiting illustrativescenario of operation of the exhaust system 600 will now be described.Different implementations of specific methods will be described in moredetail with reference to FIGS. 21 to 23. It should be noted that this issimply one non-limiting example to provide a high-level understanding ofthe general operation of the exhaust system 600, and differentimplementations and details will be set out below.

Broadly stated, the system controller 500 retrieves predeterminedpositions of the valve 630 from data tables (datasets) based on throttleposition (TPS) and engine speed (RPM). Depending on the particular modeof operation (described further below), the exhaust pressure, inputpressure, or a difference between the two are simultaneously monitoredby comparing their values to similar predetermined pressure datasets. Aflow-chart 950 generally depicting the steps taken by the systemcontroller 500 when controlling the valve 630 in the presentillustrative scenario is illustrated in FIG. 31.

First, the controller 500 determines whether the snowmobile 10 is beingoperated near sea-level or nearer to a high altitude. The relativealtitude (high or low) is generally determined by the intake pressuresensor 504 by measuring the ambient air pressure entering the air intakesystem, but in some cases the snowmobile 10 could include an altimetercommunicatively connected to the system controller 500 for determiningthe altitude. The system controller 500 can then retrieve thepredetermined datasets of valve position and pressure corresponding tooperation of the snowmobile 10 at the relevant altitude range. In orderto avoid inaccurate altitude readings by the intake pressure sensor 504caused by additional pressure created by the turbocharger 300, thealtitude-related pressure reading is taken when the RPM and the TPSoutputs are below a predetermined level that corresponds to an operatingstate of the snowmobile 10 where no boost pressure from the turbocharger300 should be created. It is also noted that datasets corresponding todifferent altitudes, other than low or high, could be used. Datasetscorresponding to more than two altitudes are also contemplated.

Following determination that the snowmobile 10 is either at high or lowaltitude, the system controller 500 then determines if the valve 630should be adjusted according to a “coarse” adjustment regime or a “fine”adjustment regime. This determination is performed by comparing anactual boost pressure (the current air intake pressure which issupplemented by the turbocharger 300) with a predetermined desired boosttarget pressure based on a dataset of TPS vs RPM. The actual boostpressure produced by the turbocharger 300 is determined by the intakepressure sensor 504. A desired boost target pressure for the current TPSand RPM values is determined from a predetermined dataset, an examplepredetermined desired boost target pressure dataset 975 being shown inFIG. 32. When the actual boost from the turbocharger 300 is within apredetermined range or threshold of the desired boost target (forexample within 5, 10, or 15 mbars of the desired boost), the fine regimewill be used. Otherwise, the coarse regime will be used. Depending onthe specific implementation, the predetermined range could be modifieddepending on factors such as ambient air temperature, altitude etc. Itis further noted that the predetermined range for switching from thecoarse regime to the fine regime could, in some cases, be different thanthe predetermined range for switching from the fine regime to the coarseregime. This hysteresis is introduced into the coarse/fine determinationapproach to aid in limiting rapid switching between the two controlregimes. If the threshold differences for switching between the coarseand fine adjustment regimes were the same, for example, each time thepressure difference is slightly below or above the threshold the methodcould switch regimes in a rapid alternation between the coarse and fineadjustment regimes. This could be unnecessarily inefficient especiallywhen the pressure difference is oscillating around the threshold value.

When operating in the coarse adjustment regime, also known as a dynamicregime, the back pressure is simultaneously monitored and controlledaccording to a pressure dataset, in order to ensure that movement of thevalve 630 to increase boost pressure does not cause a detrimentalincrease in back pressure. A sample pair of a valve position dataset 960and a pressure dataset 970 are illustrated in FIG. 33 (the values aresimply illustrative and are not meant to be limiting). In the case wherepressure dataset 970 is being used in the coarse regime, the outputvalues will represent a maximum value difference between the exhaustpressure and the intake pressure as will be described in more detailbelow.

During control of the valve 630, if the back pressure rises above acertain amount for the current operating conditions (e.g. RPM and TPS),the performance of the engine 26 could be negatively affected or atleast not optimal. To impede this from happening, the representation ofthe maximum back pressure as determined in the dataset 970 from thecurrent TPS and RPM values, is compared to the actual back pressure, asdetermined from the exhaust pressure minus the intake pressure obtainedfrom the exhaust pressure sensor 590 and the intake pressure sensor 504respectively. If the actual back pressure exceeds the value from thedataset 970, the system controller 500 will apply a correction to thevalve position dataset 960 in order to move the valve 630 to a positionthat maintains the back pressure within an acceptable range, i.e. theactual pressure difference below that obtained from the dataset 970. Insome cases a correction factor could be mathematically determined andapplied across the dataset 960. For instance, the correction factorcould be determined based on the difference between the value retrievedfrom the dataset 970 and the actual back pressure as determined from thepressures measured by the exhaust and intake pressure sensors 590, 504.Notably, the correction factor could be proportional to the differencebetween the value retrieved from the dataset 970 and the actual backpressure as determined from the pressures measured by the exhaust andintake pressure sensors 590, 504. In some implementations, rather thandetermining a correction factor, a different predetermined dataset 960could be retrieved.

It is to be understood that, in order for the calculation of the actualback pressure to be accurate, the amount of time lapsed between themeasurements made by the exhaust pressure sensor 590 and the intakepressure sensor 504 should be kept relatively small such that themeasurements are made generally simultaneously. Notably, the pressuresat the locations of the sensors 590, 504 can change rapidly andtherefore if a significant amount of time is allowed to lapse betweenthe measurement made by the exhaust pressure sensor 590 and thecorresponding measurement made by the intake pressure sensor 504, thecorrection made to the position of the valve 630 may not be veryaccurate to obtain the desired back pressure. For instance, the exhaustpressure sensor 590 and the intake pressure sensor 504 makecorresponding measurements within one revolution of the crankshaft 126from one another. More specifically, in this embodiment, the exhaustpressure sensor 590 and the intake pressure sensor 504 makecorresponding measurements within a tenth of a revolution of thecrankshaft 126 from one another. The exhaust pressure sensor 590 and theintake pressure sensor 504 may make corresponding measurements between atenth of a revolution of the crankshaft 126 and one revolution of thecrankshaft 126 from one another but other frequencies are contemplated.

In the fine adjustment regime, fine adjustment tables, also referred toas static datasets, are used when there is a small difference betweenthe actual boost pressure and the desired boost pressure as mentionedabove. In contrast to the approach taken in coarse adjustment, the fineadjustments are made to approach and maintain the optimal intakepressure (boost pressure) into the engine 26. As small adjustments tothe position of the valve 630 should not have a drastic effect on theback pressure, during the fine adjustment regime the back pressure maynot be continuously monitored, as it is in the coarse regime. As withthe coarse regime, the fine regime uses a valve position dataset similarto that of dataset 960, which is based on the actual TPS and RPM values,and a pressure dataset similar to that of 970 also based on the actualTPS and RPM values. The pressure dataset 970, when in the fine regime,includes values that represent only the intake pressure and that are tobe compared to the actual intake pressure measure by the intake pressuresensor 504. The difference between the output from the dataset 970, whenin the fine regime, and that of the actual intake pressure, willdetermine a correction factor to be applied to the valve position fromdataset 970.

During operation, the system controller 500 continuously reevaluates thealtitude and coarse/fine determinations, as there will be changes to thethrottle and RPM positions as the snowmobile 10 is operated, which willalso change the exhaust and intake pressures as the valve 630 iscontrolled to improve operation of the engine 26, and/or changes in thealtitude at which the snowmobile 10 is being operated as it travels overterrain.

With reference to FIGS. 21 to 23, different methods of controlling theflow of exhaust gas from the engine 26 will be described. Each will bedescribed in more detail below. Briefly, the methods 700, 750, 800 aimto balance providing optimized boost to the engine 26 based on operatingconditions (in the form of compressed air provided by the turbocharger300) with the detrimental increase of back pressure that can be causedwhile the turbocharger 300 is spooling up. This control is provided bythe valve 630. As is briefly mentioned above, operation of the exhaustsystem 600 with the valve 630 assists in preventing back pressure fromimpeding engine functionality, as the exhaust gas flows out through thebypass conduit 620. By closing the valve 630, exhaust gas is directedinto the exhaust turbine 350 such that the turbocharger 300 providesadditional air to the engine 26, but this exhaust flow path 675 alsoincreases the back pressure. In some implementations of the methods,adjustments can be made to the positioning of the valve 630 to balancethe need for additional compressed air versus negatively impactingengine operation through increased back pressure.

Operation Based on a Pressure Reading

Operation of the exhaust system 600 in accordance with different methodsaccording to the present technology will now be described in moredetail. In reference to FIG. 21, a non-limiting implementation ofcontrolling operations in the exhaust system 600 is set out in the formof a method 700 for controlling a flow of exhaust gas from the engine26. The method 700 is performed by the system controller 500 accordingto the present technology. In some implementations, it is contemplatedthat an additional or substitute computational system could beimplemented to perform the method 700.

The method 700 begins at step 705, with determining at least onepressure of the engine 26. Based on one or more of the pressuresdetected for the engine 26, the method 700 determines how to positionthe valve 630 in order to optimize or improve performance of the engine26. As will be described in more detail below, the valve 630 could bepositioned based on, but is not limited to, exhaust pressure, air intakeand/or atmospheric pressure, and the desired or actual boost pressure.

The method 700 then continues at step 720 with moving the valve 630 tothe closed position, the open position, or an intermediate positionbased at least on the pressure determined in step 710. Depending on thedetermined pressure, the valve 630 is moved to direct more or lessexhaust gas into the exhaust turbine 350. In some cases, the desiredposition of the valve 630 will correspond to the current position of thevalve 630, and as such the valve 630 would not be moved.

In some implementations, determining a pressure at step 705 includesdetermining a pressure differential between an actual boost pressure ofair flowing into the engine 26 and a predetermined boost pressure of airflowing into the engine 26 at sub-step 710.

In some implementations, the determining the pressure differential atsub-step 710 is performed in two sub-steps. First the actual boostpressure is determined at sub-step 712. The actual boost pressure isdetermined based on readings from the intake pressure sensor 504, todetermine the air intake pressure coming from the turbocharger 300. Itis contemplated, however, that a different sensor and/or operationalvalue could be used to determine the actual boost pressure.

The predetermined boost pressure is determined at sub-step 714. Thepredetermined boost pressure is a boost pressure calculated orpreviously determined to be matched generally to the operatingconditions of the engine 26, such that operation of the engine 26 isbest optimized. The predetermined boost pressure is retrieved from acomputer-accessible storage medium 507 operatively connected to orincluded in the system controller 500 (shown schematically in FIG. 8).It is contemplated that additional sensors could be included in theexhaust system 600 and utilized in the method 700.

In some implementations, determining the predetermined boost pressure atsub-step 714 includes at least one of: determining, by the engine sensor586, the engine speed of the engine 26, determining a throttle valveposition of the throttle valve 39 of the engine 26 by the throttle valveposition sensor 588, determining a throttle lever position by theposition sensor of the throttle lever 86, and determining a rate ofthrottle valve opening of the throttle valve 39. In someimplementations, the rate of throttle valve opening could be determinedinstead or in addition to determining the throttle valve position. Thepredetermined boost pressure is then retrieved from the computer-basedstorage medium 507, based on the determined engine speed, throttle valveposition, throttle lever position, and/or rate of throttle valveopening.

It is contemplated that the sub-steps 712, 714 could be performed in anyorder or simultaneously, depending on the specific implementation and/oroperational scenario. In some implementations, it is contemplated thatthe snowmobile 10 could include a differential sensor for determiningthe pressure differential at sub-step 710 in a single measurement.

In some implementations or iterations, the method 700 could furtherinclude determining that the difference between the predetermined boostpressure and the actual boost pressure, as determined in sub-step 710,is less than a difference threshold. The difference threshold generallyindicates whether movement of the valve 630 in order to bring the actualboost pressure more closely in line with the predetermined boostpressure will need to be a coarse adjustment (if the difference is abovethe threshold) or only needs to be a fine adjustment (if the differenceis below the threshold).

Based on the difference being less than the difference threshold, themethod 700 then continues with determining a desired valve position ofthe valve 630 from a fine adjustment data set. The fine adjustment dataset, based on at least one of the throttle position and the engine speedas determined above, relates to fine, or minor, adjustments to theposition of the valve 630 needed in order to provide the desiredpressure in the engine 26 by decreasing the difference between thepredetermined boost pressure and the actual boost pressure. The method700 then continues with moving, following determining the desired valveposition, the valve 630 toward the desired valve position.

Based on the difference being greater than the difference threshold, themethod 700 then similarly continues with determining a desired valveposition of the valve 630 from a coarse adjustment data set. The coarseadjustment data set, based on at least one of the throttle position andthe engine speed as determined above, relates to coarse, or larger,adjustments to the position of the valve 630 needed in order to providethe desired pressure in the engine 26 by decreasing the differencebetween the predetermined boost pressure and the actual boost pressure.The method 700 then continues with moving, following determining thedesired valve position, the valve 630 toward the desired valve position.

In some implementations, the method 700 could be done iteratively, suchthat when the difference between the predetermined boost pressure andthe actual boost pressure is large, coarse adjustments are made toreduce the difference. Once the difference between the predetermined andactual boost pressure are reduced below the threshold, then fineadjustments would be used. Use of coarse and fine adjustments is simplyone non-limiting example of controlling adjustment of the position ofthe valve 630. It is also contemplated that the adjustments could bepartitioned into three or more datasets. For example, two thresholdscould be used to split the adjustments into “large coarse adjustments”,“small coarse adjustments”, and “fine adjustments”. It is alsocontemplated that a single data set could be utilized for determining adesired valve position.

In some implementations or iterations of the method 700, the determiningthe pressure differential at sub-step 710 includes determining adifference between an intake air pressure of air flowing to the engine26, and an exhaust gas pressure of exhaust gas flowing out of the engine26, in place of determining the difference between predetermined andactual boost pressures. In such an implementation, the method 700 wouldthen include determining the intake air pressure by the intake pressuresensor 504 and determining the exhaust gas pressure by the exhaustpressure sensor 590.

The method 700 would then further include determining a predeterminedpressure differential between the exhaust gas pressure and the intakeair pressure. Similar to the predetermined boost pressure, thepredetermined pressure differential corresponds to the optimal orpreferred difference between the exhaust and intake air pressures whichcorrespond to better operation of the engine 26 for the currentoperating conditions. For example, the predetermined pressuredifferential could be set based on engine parameters such as enginespeed such that the engine 26 generally has the air volume necessary forproper functioning, without creating too much back pressure. In someimplementations, the predetermined pressure differential could bedetermined based on, but is not limited to: throttle position and enginespeed.

In such an implementation, the method 700 then continues withdetermining that a difference between the pressure differential and thepredetermined pressure differential is non-zero. The non-zero differenceindicates simply that the actual pressure differential is not at thepredetermined pressure differential and thus the engine 26 may not beoperating optimally. The method 700 thus then continues with moving thevalve 630 based on the difference being non-zero to the open position,the closed position, or one of the intermediate positions. In someimplementations, the position to which the valve 630 is moved coulddepend on whether the actual pressure differential is greater or lessthan the predetermined pressure differential.

In some implementations or iterations of the method 700, the method 700includes determining that the intake air pressure is below a thresholdatmospheric pressure. As with the above steps, determination of theintake air pressure includes measurement of the pressure by the airintake pressure sensor 504. The system controller 500 could thendetermine if the measured air pressure of air entering the engine 26 isbelow some predetermined threshold. For example, the threshold could beset based on engine parameters such that the engine 26 generally has theair volume necessary for proper functioning. It is also contemplatedthat the threshold atmospheric pressure may be a predetermined range ofatmospheric pressure. In one non-limiting example, intake air pressurecould fall below the threshold when the snowmobile 10 is climbing amountain and increasing in altitude.

Then, based at least on the intake air pressure being below thethreshold atmospheric pressure, the method 700 could continue withmoving the valve 630 to or toward the closed position (if the valve 630is in either the open or intermediate position). This would begin, orincrease, operation of the turbocharger 300. As such, when the engine 26is not getting sufficient air for good or sufficient operation, forinstance when the snowmobile 10 is being operated at high altitudes, theturbocharger 300 can be spooled up to provide compressed air to theengine 26 (as is described above).

In some implementations or iterations of the method 700, the method 700could further include determining that the back pressure is too high andopening up the valve 630 to maintain a balance between increasing intakeair pressure to the engine 26 and allowing back pressure to ease throughopening of the valve 630.

Subsequent to moving the valve 630 to or toward the closed position, themethod 700 could further include determining that the exhaust gaspressure is above a threshold exhaust gas pressure. As is mentionedabove, the exhaust gas pressure is measured by the exhaust pressuresensor 590; the system controller 500 then compares the measurement tothe determined back pressure threshold.

Based on the exhaust gas pressure being above the threshold exhaust gaspressure, the method 700 then continues with repositioning the valve 630to either the open position or an intermediate position such thatexhaust gas flows at least partially along the bypassing exhaust gasflow path 670. By opening up the valve 630 such that an increasedportion of the exhaust gas flows out through the bypass portion 620, theback pressure is eased. Depending on the iteration of the method 700,the valve 630 could be moved to only a small degree, or in some casesmoved all the way to the open position. In some implementations, thechange in position of the valve 630 could be proportional or directlyrelated to an increase of exhaust gas pressure after moving the valve630 to the closed position.

In some implementations or iterations of the method 700, the valve 630could be moved back to the open position once the snowmobile 10 isoperated at atmospheric pressures above the threshold used above tobegin use of the turbocharger 300. In one non-limiting example, thevalve 630 could be opened back up, partially or fully to the openposition, when the snowmobile 10 decreases in altitude and theatmosphere surrounding the snowmobile 10 becomes richer.

In such a scenario, the method 700 could further include determining (bythe intake pressure sensor 504 and the system controller 500) that theintake air pressure is above the threshold intake air pressure,subsequent to moving the valve 630 to or toward the closed position.Then, based on the intake air pressure being above the threshold intakeair pressure, the method 700 could continue with moving the valve 630such that a majority or more of the exhaust gas flows along the bypassexhaust flow path 670.

It is contemplated that the method 700 could include additional ordifferent steps, either to perform additional functions and/or toperform the steps described above. It is also contemplated that thesteps described above could be performed in an assortment of differentsequences, depending on for example user preferences, and is not limitedto the order set forth in the explanation above.

Operation Based on Exhaust Gas Pressure

In reference to FIG. 22, a non-limiting implementation of controllingoperations in the exhaust system 600 is set out in the form of a method750. The method 750 is performed, at least in part, by the systemcontroller 500 according to the present technology. In someimplementations, it is contemplated that an additional or substitutecomputational system could be implemented to perform the method 750.

The method 750 begins at step 760 with determining that an exhaust gaspressure of air flowing out of the engine 26 is above a thresholdexhaust gas pressure, where the valve 630 is in either the closedposition or an intermediate position, where a majority of the exhaustgas is flowing along the turbine exhaust flow path 675. The exhaust gaspressure is determined by the exhaust pressure sensor 590 and the systemcontroller 500 in the present implementation, as is noted above. In someimplementations, the valve 630 could have been moved to the closedposition based on a decrease in atmospheric pressure surrounding thesnowmobile 10, similar to the scenario described above in relation tothe method 700. It is also contemplated that the valve 630 could havebeen moved to or toward the closed position for an alternative reason.For one non-limiting example, the valve 630 could have been moved to theclosed position to provide more air to the engine 26, via the aircompressor 310, based on insufficient performance of the engine 26.

The method 750 then continues, at step 760, with moving the valve 630 toeither the open position or toward the open position to an intermediateposition, based on the exhaust gas pressure being above the thresholdexhaust gas pressure.

It is contemplated that the method 750 could be performed intandem/consecutively to the method 700, operation of the snowmobile 10could include implementations of both of the methods 700, 750.

It is contemplated that the method 750 could include additional ordifferent steps, either to perform additional functions and/or toperform the steps described above. It is also contemplated that thesteps described above could be performed in an assortment of differentsequences, depending on for example user preferences, and is not limitedto the order set forth in the explanation above.

Operation Based on Engine Speed and Throttle Position

In reference to FIG. 23, another non-limiting implementation ofcontrolling operations in the exhaust system 600 is set out in the formof a method 800 for controlling the flow of exhaust gas from the engine26. The method 800 is performed by the system controller 500 accordingto the present technology. In some implementations, it is contemplatedthat an additional or substitute computational system could beimplemented to perform the method 800.

In addition to controlling the position of the valve 630 to manageintake and exhaust pressures based on environmental conditions (i.e.atmospheric pressure), the exhaust system 600 is further operable toadjust exhaust gas flow to balance providing additional boost whilelimiting back pressure when the user of the snowmobile 10 requestsadditional power from the snowmobile 10.

In one non-limiting scenario, the method 800 could be implemented in asituation where the throttle lever 86 is moved to make a high powerrequest to the engine 26, for example during acceleration of thesnowmobile 10. As will be outlined in the steps below, the valve 630 ismoved to the closed position, to spool up the turbocharger 300, inresponse to this movement of the throttle lever 86. With theturbocharger 300 in use, the engine 26 would then benefit from a denserintake air charge and would have increased power output compared to asimilar engine that would be naturally aspirated. As will further bedescribed below, requesting too much boost and directing all exhaust gasalong the turbine exhaust flow path 675 may also cause the back pressureto build beyond an optimized level to the desired engine operation. Insuch a situation, the method 800 can further move the valve 630 backtoward the open position in order to allow some exhaust gas to bypassthe exhaust turbine 350, thus decreasing the back pressure.

The method 800 begins at step 810 with determining, by the engine sensor586, the engine speed of the engine 26. The method 800 then continues,at step 820, with determining a throttle valve position of the throttlevalve 39 of the engine 26. The position of the throttle valve 39 issensed by the throttle valve position sensor 588, as is mentioned above.

In some implementations, step 820 could include determining a rate ofthrottle valve opening of the throttle valve 39 instead or in additionto determining the throttle valve position. The throttle valve positionsensor 588, alone or in conjunction with the system controller 500,could also be used to measure the rate of throttle valve opening in someimplementations. The steps 810, 820 may be performed in either order, orsimultaneously, depending on the specific implementation.

The method 800 then continues, at step 830, with moving the valve 630 tothe open position, the closed position, or any intermediate position,based on the engine speed and the throttle valve position determined insteps 810, 820, as well as the starting position of the valve 630. Inthe method 800, the throttle valve position is taken into considerationto assist in controlling the exhaust gas flow for managing operation ofthe engine 26.

In some implementations or iterations, the method 800 could furtherinclude moving the valve 630 based on a temperature of the exhaust pipe202, in addition to the engine speed and the throttle valve positiondetermined in steps 810, 820. The temperature of the exhaust pipe 202 isreceived by the system controller 500 from the temperature sensor 512.In some implementations, moving the valve 630 could be basedadditionally or alternatively on the temperature of the exhaust gaswithin the exhaust pipe 202, as sensed by the temperature sensor 512.

In some implementations, the method 800 could further includedetermining a pressure differential and further moving the valve 630based on the pressure differential. In some implementations, thepressure differential is determined by comparing a predetermined boostpressure of air flowing into the engine 26 against an actual boostpressure of air flowing into the engine 26. The predetermined boostpressure, described above in more detail, is determined based at leaston one of the throttle position and the engine speed, as determined insteps 810, 820 and corresponds to what the boost pressure should beflowing into the engine 26 based on the throttle position and/or theengine speed. The actual boost pressure of air flowing into the engine26 is determined by measuring the air intake pressure by the intakepressure sensor 504 and the system controller 500, as is describedabove. In some implementations, the actual boost pressure could bedetermined differently.

In some implementations, the method 800 could further includedetermining if the engine 26 is operating at a low altitude or a highaltitude (i.e. that the snowmobile 10 is being operated at low or highaltitude) prior to moving the valve 630. In some implementations,determining if the engine 26 is operating at low altitude or highaltitude includes determining an atmospheric pressure of air enteringthe snowmobile by the intake pressure sensor 504. It is alsocontemplated that the system controller 500 could include or becommunicatively connected to an altimeter or similar altitude measuringdevice.

Upon determining that the engine 26 is operating at low altitude, themethod 800 could then continue with retrieving a desired valve positionfor the valve 630 from a low altitude data set. Upon determining thatthe engine 26 is operating at high altitude, the method 800 could thensimilarly continue with retrieving the desired valve position for thevalve 630 from a high altitude data set. In some implementations, thelow altitude data set and the high altitude data set could be stored inthe storage medium 507 communicatively connected to or part of thesystem controller 500.

The desired valve position retrieved from the low or high data setsgenerally corresponds to an optimized or predetermined valve positionbased on the altitude and the engine speed and/or the throttle position,such that air flow into the engine 26 is matched to the operatingconditions of the engine 26. In such an implementation, havingdetermined a desired position of the valve 630, moving the valve 630 atstep 830 would be performed by moving the valve 630 to the desiredposition.

In some implementations or iterations, the method 800 could furtherinclude determining, based at least on the throttle position and theengine speed determined in steps 810, 820, a threshold pressuredifferential of the engine 26. The method 800 then continues withdetermining an actual pressure differential of the engine 26. In someimplementations, determining the actual pressure differential includesdetermining the exhaust pressure downstream of the engine 26 by theexhaust pressure sensor 590, determining the air intake pressureupstream of the engine 26 by the intake pressure sensor 504, anddetermining the difference thereof.

The method 800 then continues with determining that the actual pressuredifferential is greater than the threshold pressure differential andmoving the valve 630 toward the open position if the valve 630 is eitherclosed or an intermediate positions. In such a case, the actual pressuredifferential being greater than the threshold pressure differentialcould indicate that there is too much air pressure moving into theengine 26. This could have detrimental effects on operation of theengine 26, and the method 800 could thus provide correction by allowingmore exhaust gas to bypass the exhaust turbine 350 by further moving thevalve 630 toward the open position.

In some implementations or iterations, the method 800 could furtherinclude determining that an intake pressure, as determined by the intakepressure sensor 504, is above an intake threshold and determining thatthe throttle valve position is beyond a valve position threshold. Forinstance, the method 800 could determine that there is too much airpressure moving into the engine 26 while the throttle valve 39 has beenopened too far. This combination could have detrimental effects onoperation of the engine 26, and the method 800 could provide correctionby allowing more exhaust gas to bypass the exhaust turbine 350 byfurther moving the valve 630 toward the open position.

Based on the intake pressure and the throttle valve position being pasttheir respective thresholds, the valve 630, could then be moved fromclosed position or an intermediate position toward the open position.This allows for a decrease in back pressure induced by either too muchair intake or requesting too much throttle too quickly.

In some implementations or iterations, the method 800 could furtherinclude moving the valve 630 toward the closed position, subsequent tomoving the valve 630 toward the open position, such that a portion ofthe exhaust gas flowing through the exhaust turbine 350 of theturbocharger 300 is increased. In such implementations, the method 800provides some tuning of the exhaust gas flow to balance boost from theturbocharger 300 while limiting detrimental effects of increased backpressure, which assists in smoothing the power increase of the engine26.

In some implementations or iterations, the method 800 could furtherinclude determining that the intake pressure is above the air intakepressure threshold, subsequent to moving the valve toward the closedposition. The method 800 could then include moving the valve 630 towardthe open position, based on the intake pressure being above thethreshold.

In some implementations or iterations, the method 800 could furtherinclude determining that the intake pressure is below the intakepressure threshold subsequent to moving the valve toward the closedposition. The method 800 could then further include moving the valve 630further toward the closed position, in order to allow further boost fromthe turbocharger 300.

In some implementations, the determining the intake air pressure couldinclude determining the intake pressure at a location downstream of theturbocharger 300 by a pressure sensor (not shown). Moving the valvecould then include selectively moving the valve based on the intakepressure determined by the pressure sensor downstream from theturbocharger 300.

In some implementations, the method 800 could further includedetermining the exhaust pressure downstream of the engine 26 by theexhaust pressure sensor 590 and moving the valve 630 toward the openposition based on the exhaust pressure being above a predeterminedexhaust pressure threshold.

In some implementations, where the rate of throttle valve opening isdetermined, the method 800 could further include determining that therate of throttle valve opening is above a threshold rate; and moving thevalve 630 toward the open position based at least on the rate ofthrottle valve opening being above the threshold rate. In such animplementation, the valve 630 is opened up, for example, when too muchthrottle is requested too quickly, in order to prevent back pressurefrom having a detrimental effect on engine operation (especially whenthe user is trying to increase power from the engine 26). In someimplementations, the method 800 could further include determining thatthe intake pressure is above the threshold intake pressure and movingthe valve 630 based on both the rate of throttle valve opening beingabove the threshold rate and the intake pressure being above thethreshold intake pressure.

It is contemplated that the method 800 could include additional ordifferent steps, either to perform additional functions and/or toperform the steps described above. It is also contemplated that thesteps described above could be performed in an assortment of differentsequences, depending on for example user preferences, and is not limitedto the order set forth in the explanation above.

As described above, various methods of controlling operation of theturbocharger 300 involve monitoring the back pressure affecting theengine 26. In view of the availability of the pressure information inthe present technology, operation of the snowmobile 10 can further beoptimized by making adjustments to the fuel-air mixture in the engine26.

Changes in the back pressure in the engine 26 and the exhaust system 600impacts the fuel to air ratio present in the engine 26. All other thingsremaining equal, the engine 26 obtains maximum power when a target backpressure is maintained. If the effective back pressure in the engine 26deviates from that target, the fuel to air ratio is affected, which inturns diminishes the operation of the engine 26.

With increasing back pressure, the total amount of air flowing throughthe engine 26 is reduced. In such a circumstance, a constant amount offuel injected would cause an increased fuel to air ratio in the engine26 and as such the engine 26 would be provided with a fuel-air mixturethat is too rich. As such, the engine 26 may not perform optimally.

Too much of a decrease in back pressure at high engine speed, all otherthings being equal, would also lead to an increase in the fuel to airratio. When back pressure is too low, pressure waves created by theexhaust pipe 202 (which aid creating a trapping effect to maintain airin a two-stroke engine) could be mistimed, and the combustion chambersof the engine 26 are emptied of more air than optimally would occur. Insuch a case, the engine 26 would again end up with a richer fuel-airmixture (receiving the same amount of fuel with less air). Once againthe engine 26 may not perform optimally.

Supplying a Fuel-Air Mixture

With reference to FIGS. 24 and 33, a method 900 of supplying a fuel-airmixture in the engine 26 of the snowmobile 10 will now be described.

The method 900 begins at step 910 with determining a pressuredifferential between an intake air pressure of air flowing toward theengine 26 and an exhaust gas pressure of exhaust gas flowing out of theengine 26. This pressure differential, as mentioned above with respectto the dynamic regime, generally correlates with the back pressure inthe engine 26. The pressure differential is determined by comparing, bythe system controller 500, measurements taken from the air intakepressure sensor 504 and the exhaust pressure sensor 590. In someimplementations, it is contemplated that the snowmobile 10 could includea differential sensor for determining the pressure differential in asingle measurement.

In some implementations of the method 900, the pressure differential isdetermined in two steps. Specifically, by determining the intake airpressure, by the air intake pressure sensor 504, at sub-step 912. Thenthe method 900 continues with determining the exhaust gas pressure, bythe exhaust pressure sensor 590, at sub-step 914. Depending on thespecific implementation, the steps 912, 914 could be performed in anyorder, or simultaneously.

The method 900 continues, at step 920, with determining an amount offuel to be injected into the engine 26 based on at least the pressuredifferential (as determined in step 910). The system controller 500calculates the amount of fuel to be injected, such that the fuel-airmixture is maintained at an appropriate value, based at least on thebackpressure in the engine 26. It is contemplated that another computingsystem could be included to manage the determination of the amount offuel to be injected, rather than the system controller 500. A base fuelinjection quantity is determined by using a dataset relating an amountof fuel to be injected corresponding to the current TPS and RPM. Anexample base fuel injection dataset 982 is shown in FIG. 34 where thebase fuel injection is indicated as a volume, in this example in mm³.

In some implementations, the base fuel injection quantity could bemodified according to the back pressure as follows. A target backpressure (the exhaust pressure less the intake pressure) is determinedfrom a dataset of TPS and RPM, such as in the example dataset 984. Theactual back pressure is obtained from the exhaust pressure minus theintake pressure using the exhaust pressure sensor 590 and the intakepressure sensor 504 respectively.

A fuel correction quantity or percentage would then be obtained from afuel correction dataset 986 of RPM and the difference between the actualback pressure and the target back pressure (identified as AAP). The fuelcorrection from this dataset 986 would then be applied to the base fuelinjection quantity to determine a final injection quantity, modifiedaccording to the measured back pressure.

The method 900 then terminates, at step 930, with injecting the amountof fuel (as determined in step 920) into the engine 26. The fuel isinjected by the fuel injectors 41, as is described above.

It is contemplated that in some implementations, the method 900 couldrecommence after step 930. In some implementations, the method 900 couldcontinue beyond step 930 with determining a changed pressuredifferential. The method 900 could then continue with determining arevised amount of fuel based on the changed pressure differential. Thisimplementation of the method 900 could then terminate with injecting therevised amount of fuel into the engine 26.

In some implementations, the method 900 could include determining thatthe pressure differential has increased, determining a reduced amount offuel to be injected, and injecting the reduced amount of fuel into theengine 26. In some implementations, the method 900 could also includedetermining that the pressure differential has decreased, determining areduced amount of fuel to be injected, and injecting the reduced amountof fuel into the engine 26.

In some implementations, the method 900 repeats following step 930, atsome predetermined time interval, to readjust the fuel-air mixture inorder to compensate for changes in the back pressure. In someimplementations, the method 900 could be performed by the systemcontroller 500 intermittently during operation of the snowmobile 10. Itis also contemplated that that method 900 could be performed only onceor only a few times during operation of the snowmobile. It is furthercontemplated that the method 900 could be performed in response to thepressure differential and/or the intake or exhaust pressures passing apredetermined threshold.

In some implementations, the method 900 could further includedetermining the engine speed, and the determining the amount of fuel tobe injected is also based on the engine speed. In some implementations,the method 900 could further include determining the throttle positionof the throttle valve 39, and the determining the amount of fuel to beinjected is further based on the throttle position.

It is further contemplated that additional variables could be taken intoaccount when determining or calculating the amount of fuel to beinjected, in addition to the pressure differential. These could include,but are not limited to: engine speed (rpm), the throttle position, theair temperature, ambient barometric pressure, close loop wide bandlambda control, and temperature of the exhaust gas.

It is contemplated that the method 900 could include additional ordifferent steps, either to perform additional functions and/or toperform the steps described above. It is also contemplated that thesteps could be performed in an assortment of different sequences,depending on the specific implementation.

Modifications and improvements to the above-described implementations ofthe present technology may become apparent to those skilled in the art.The foregoing description is intended to be exemplary rather thanlimiting. The scope of the present technology is therefore intended tobe limited solely by the scope of the appended claims.

What is claimed is:
 1. A snowmobile comprising: a frame; at least oneski connected to the frame; an engine supported by the frame, the enginehaving an engine air inlet and an exhaust outlet; an exhaust pipefluidly connected to the exhaust outlet of the engine; a turbochargerfluidly connected to the exhaust pipe, the turbocharger including: anexhaust turbine, and a housing the exhaust turbine; a bypass conduitdisposed upstream of the housing and fluidly communicating with thehousing, the bypass conduit including an exhaust inlet fluidly connectedto the exhaust pipe; a valve disposed in the bypass conduit forselectively controlling the flow of exhaust gas through theturbocharger, the valve being selectively movable between at least afirst position and a second position; and an exhaust collector fluidlyconnected to the turbine housing and the bypass conduit for receiving aflow of exhaust gas therefrom, a first exhaust flow path being definedfrom the exhaust inlet to the exhaust collector, exhaust gas flowingalong the first exhaust flow path passing through the exhaust inlet,then through the bypass conduit, and then into the exhaust collector, asecond exhaust flow path being defined from the exhaust inlet to theexhaust collector, exhaust gas flowing along the second exhaust flowpath passing through the exhaust inlet, then through the bypass conduit,then through the exhaust turbine, and then into the exhaust collector,in the first position of the valve, at least a majority of the exhaustgas flowing along the first exhaust flow path, in the second position ofthe valve, at least a majority of the exhaust gas flowing along thesecond exhaust flow path.
 2. The snowmobile of claim 1, wherein thevalve is selectively moved to the second position when the engine isoperated below a threshold atmospheric pressure.
 3. The snowmobile ofclaim 1, wherein: the valve is further selectively movable to at leastone intermediate position between the first and second positions; and inthe at least one intermediate position, the exhaust gas flows along bothof the first exhaust flow path and the second exhaust flow path.
 4. Thesnowmobile of claim 1, wherein: the turbocharger further comprises anair compressor fluidly connected to the engine air inlet; and thesnowmobile further comprises an air intake system fluidly connectingatmosphere to the engine, the air intake system including: the aircompressor, and the engine air inlet.
 5. The snowmobile of claim 1,wherein: the exhaust collector includes a single collector outlet; andthe snowmobile further comprises a muffler fluidly connected to thecollector outlet, the muffler receiving the exhaust gas from both thefirst exhaust flow path and second exhaust flow path via the collectoroutlet.
 6. The snowmobile of claim 1, wherein: the exhaust collectorincludes a collector outlet; and the snowmobile further comprises amuffler fluidly connected to the collector outlet, the muffler having asingle muffler inlet for receiving exhaust gas from both the firstexhaust flow path and second exhaust flow path via the collector outlet.7. The snowmobile of claim 1, wherein the exhaust collector includes: atleast one inlet for receiving exhaust gas flow, the at least one inletincluding: a first portion for receiving exhaust gas flowing along thefirst exhaust flow path; and a second portion for receiving exhaust gasflowing along the second exhaust flow path, the first portion and thesecond portion being integrally connected.
 8. The snowmobile of claim 1,wherein: the engine includes: a throttle valve, and a throttle valveposition sensor operatively connected to the throttle valve; and thevalve is selectively moved based at least on a throttle valve positiondetermined by the throttle valve position sensor.
 9. The snowmobile ofclaim 1, wherein: the engine includes: a throttle valve, and a throttlevalve position sensor operatively connected to the throttle valve; andthe valve is selectively moved based at least on a rate of change of athrottle valve position, the rate of change being determined by thethrottle valve position sensor.
 10. The snowmobile of claim 1, wherein:the bypass conduit includes a passage through which exhaust gas flowswhen flowing along the first exhaust flow path; the exhaust turbine hasa turbine inlet through which exhaust gas flows when flowing along thesecond exhaust flow path; and a cross-sectional area of the passage islarger than a cross-sectional area of the turbine inlet of theturbocharger.
 11. The snowmobile of claim 1, wherein a change ofdirection of exhaust gas flowing from an outlet of the exhaust pipealong the second exhaust flow path is greater than for exhaust gasflowing from the outlet of the exhaust pipe along the first exhaust flowpath bypassing the exhaust turbine.
 12. A snowmobile comprising: aframe; at least one ski connected to the frame; an engine supported bythe frame, the engine having an engine air inlet and an exhaust outlet;an exhaust pipe fluidly connected to the exhaust outlet of the engine; aturbocharger fluidly connected to the exhaust pipe, the turbochargerincluding: an exhaust turbine, and a housing the exhaust turbine; abypass conduit disposed upstream of the housing and fluidlycommunicating with the housing, the bypass conduit being fluidlyconnected to an outlet of the exhaust pipe; a valve disposed in thebypass conduit for selectively controlling the flow of exhaust gasthrough the turbocharger by selectively closing a bypass passage withinthe bypass conduit, the valve having at least a bypass position foropening the bypass passage and directing exhaust gas to bypass theexhaust turbine; and an exhaust collector fluidly connected to thebypass conduit for receiving a flow of exhaust gas therefrom, at least aportion of an inlet of the exhaust collector being contained within aprojection of the outlet of the exhaust pipe, the projection being takenalong an axis normal to the outlet of the exhaust pipe.
 13. Aturbocharger assembly for fluidly connecting to an exhaust pipe, theassembly comprising: a turbocharger including: an exhaust turbine, and ahousing the exhaust turbine; and a bypass conduit disposed upstream ofthe housing and fluidly communicating with the housing, the bypassconduit including: a conduit inlet for receiving exhaust gas from theexhaust pipe, the conduit inlet being defined by the bypass conduit, theconduit inlet defining a flow axis through a center of the conduitinlet, the exhaust gas flowing into the conduit inlet flowing generallyparallel to the flow axis; a bypass passage defined by the bypassconduit, the bypass passage forming a fluid connection between theconduit inlet and a bypass outlet defined by the bypass conduit; a valvedisposed in the bypass conduit for selectively controlling the flow ofexhaust gas through the bypass passage, the valve being selectivelymovable between at least an open position and a closed position; and aturbocharger passage defined by the bypass conduit, the turbochargerpassage forming a fluid connection between the conduit inlet and theexhaust turbine, the conduit inlet and an inlet of the bypass passagebeing at least partially aligned such that at least a portion of theexhaust gas entering the conduit inlet parallel to the flow axis flowsunobstructed into the bypass passage when the valve is in the openposition.
 14. The turbocharger assembly of claim 13, wherein, when thevalve is in the closed position, at least a portion of the valve iscontacted by the exhaust gas entering through the conduit inlet andflowing parallel to the flow axis.
 15. The turbocharger assembly ofclaim 13, wherein, when the valve is in a position intermediate the openposition and the closed position, at least a portion of the valve iscontacted by the exhaust gas entering through the conduit inlet andflowing parallel to the flow axis.
 16. A conduit for fluidly connectingto a turbocharger housing, the conduit comprising: an inlet conduitportion for receiving exhaust gas from an exhaust pipe; an inlet definedby the inlet conduit portion, exhaust gas from the exhaust pipe enteringthe inlet conduit portion through the inlet, the inlet defining acentral axis normal to the inlet and through a center of the inlet; afirst outlet conduit portion; a second outlet conduit portion; and aflow divider disposed between the first outlet conduit portion and thesecond outlet conduit portion, the flow divider being disposed betweenthe central axis and one of the first outlet conduit portion and thesecond outlet conduit portion.
 17. The conduit of claim 16, wherein: theinlet conduit portion, the first outlet conduit portion, and the secondoutlet conduit portion are integrally connected; and the inlet conduitportion, the first outlet conduit portion, and the second outlet conduitportion form a generally Y-shaped conduit.
 18. The conduit of claim 16,wherein: the inlet is a circle; and the central axis passes through thecenter of the circle.
 19. The conduit of claim 16, wherein: the firstoutlet conduit portion is fluidly connected to a turbocharger disposedwithin the turbocharger housing; exhaust gas exiting the conduit throughthe second outlet conduit portion bypasses the turbocharger; and theflow divider is disposed between the central axis and the second outletconduit portion.
 20. The conduit of claim 16, further comprising: avalve disposed in the second outlet conduit portion; and wherein thevalve is selectively movable between at least: a first position allowingexhaust gas to enter the second outlet conduit portion, and a secondposition blocking exhaust gas from entering the second outlet conduitportion.
 21. A turbocharger assembly for fluidly connecting to anexhaust pipe, the assembly comprising: a turbocharger including: anexhaust turbine, a turbocharger inlet defined by the exhaust turbine,and a housing the exhaust turbine; and a bypass conduit disposedupstream of the housing and fluidly communicating with the housing, thebypass conduit including: a conduit inlet for receiving exhaust gas fromthe exhaust pipe; a bypass passage forming a fluid connection betweenthe conduit inlet and a bypass outlet defined by the bypass conduit, thebypass passage including an opening; and a turbocharger passage forminga fluid connection between the conduit inlet and the turbocharger inlet,an area of the opening being between 0.75 and 1.25 times an area of theturbocharger inlet.
 22. The turbocharger assembly of claim 21, whereinthe area of the opening is greater than the area of the turbochargerinlet.
 23. The turbocharger assembly of claim 21, wherein the area ofthe turbocharger inlet is greater than the area of the opening.